Abstract:
A hard cover for the open bed of a pickup truck is thermoformed from two sheets of heat deformable plastic material. The top sheet has a slightly crowned surface and four depending walls defining a perimeter lip corresponding to the top ledge of a pickup truck bed. The bottom sheet reinforces the top sheet and is itself slightly crowned and includes four walls. The bottom sheet includes prop support members which depend below the margin defined by the perimeter lip of the hard cover. The perimeter lip of the hard cover may be adapted to reside within a range of similarity sized pickup truck bed rail margins, so that one hard cover can be utilized on several truck models. The hard cover may also be associated with a molded platform that overlays and closely conforms to the bed rails of a truck bed to provide a protective truck bed cover assembly. The molded platform is provided with a channel to receive the lip of the hard cover to provide a seal. The hard cover is releasibly attached to the molded platform, and the molded platform itself is adapted for direct installation to the truck bed. The molded platform is an intermediate interface between the hard cover and the truck bed. The molded platform protects the truck bed rail against damage when the present hard cover is supported upn the truck bed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit to U.S. Provisional Ser. No. 60/140,741 dated Jun. 25, 1999. 
    
    
     FIELD OF THE INVENTION 
     This invention is generally directed toward a top for a land vehicle. More particularly, this invention is directed to a rigid cover for a pickup truck cargo bed. The present cover is composed of a first thermoformed sheet of plastic that provides a desirable application surface, and a second thermoformed sheet of plastic comprising molded-in details imparting strength, encapsulating hardware and other functional elements that advance the art of tops for land vehicles. 
     In the present embodiments, the first and second thermoformed sheets are permanently bonded together to produce a one-piece cover. Also included are one or more hinge elements operable to connect the cover to the truck bed about front wall; one or more props which support the cover in the opened position; and, a lock mechanism to secure the cover in the closed position. 
     DESCRIPTION OF THE PRIOR ART 
     Pickup truck vehicles are used for both work-related activities and personal transportation. The pickup truck bed provides carrying space for both work-related and personal cargo. In order to prevent cargo from being damaged by weather or stolen, it has become common to install a protective cover over the truck bed. There are four types of cover commonly available for this purpose. The most popular type of cover is referred to by industry as a “topper” or a “truck cap”. A topper is characterized as having two opposed vertical side walls, a front wall and a back wall, which walls extend upward from the truck bed rails to form a roof with an over-all height generally equal to the top of passenger cabin of the pickup truck vehicle. The opposed sidewalls generally include windows for visibility, and the back wall includes a rear window lift gate for access. The three other types of covers for a truck bed are generically referred to as tonneau covers. The three types of tonneau cover comprise one-piece rigid covers; multi-piece sectional and roll-up covers; and, soft covers composed of a flexible vinyl fabric supported by cross-bows and optionally, a perimeter fabricated metal frame. The present invention falls under the category of one-piece rigid covers. 
     There are several prior art devises that disclose one-piece rigid tonneau covers. These prior art devises in turn include fiberglass reinforced plastic (FRP) covers; composite thermoset plastic covers and fabricated metal and/or plastic panel covers. By a considerable margin, the most popular and widely sold one-piece rigid covers are the FRP cover variety. 
     FRP cover products are produced by conventional lay-up operations are uneconomical compared to the modern technology of thermoform manufacturing operations. 
     The lay-up operation is time-consuming and labor intensive. The lay-up process involves the application of parting agents, a gel coat surface and two or more lamination steps that often include inserts for reinforcement. Each step is labor intensive and requires cure times that are influenced by temperature, humidity and other technical and labor factors. A single FRP tonneau cover mold is capable of producing 3-5 parts in a 24-hour period. Current thermoforming art is capable of converting sheets of plastic into rigid one-piece twin-sheet covers at a rate of 12 plus parts per hour. Thermoforming is a significantly more productive processing technology. 
     The lay-up operation uses polyester resins and fiberglass. The application surface of the lay-up process comprises specialty gel-coat resins that normally cost double the price of the polyester resins. An FRP cover for a small size pickup truck bed weighs approximately 95 lbs. The weight of the center of an FRP cover is so heavy that it collapses in upon itself when unsupported. Therefore, contemporary FRP covers also included filled resins and/or load-bearing inserts comprising wooden or aluminum cross members, foam panels or paperboard honeycomb panels that become saturated with resin between two laminations of FRP. A twin-sheet thermoformed plastic cover, for the equivalent make and model of pickup truck bed weighs 60 lbs. The resin costs for thermoformable plastics range in price, with HDPE at the low end and ABS at the high end. The material cost factor between FRP and thermoformable resins is in the order of 2 to 1. Thermoforming is therefore a much more economical processing technology. 
     The lay-up operation produces styrene monomer vapors that produce worker safety and environmental problems. The lay-up operation also poses cleanup and storage problems. The lay-up operation is taxed by many states to dis-incentivise its use and to re-cover its impact costs upon society. The thermoforming process of converting HDPE or ABS plastic resins into finish products carries little, if any risk, to society. Unlike thermosetting FRP resins, HDPE and ABS are 100% recyclable. Thermoforming is therefore a safer and cleaner processing technology. 
     The FRP lay-up operation has retained its prevalent position within the market because the manufacturers of tonneau covers also manufacture FRP toppers. The larger topper market, in terms of manufacturers&#39; sales revenue, has therefore precluded the move toward more promising thermoforming technologies. In summary, the existing manufacturers operate within a competitive market and are therefore reluctant to switch to more modern operations and technologies. 
     In addition to being uneconomical and having negative worker safety and environmental impacts, FRP covers are also not user friendly. The heavy weight construction of a FRP cover poses several problems. The FRP cover can not be easily removed from the truck bed because it of its heavy weight. A heavy weight FRP cover also increases fuel consumption and the cost of operating the vehicle. The heavy weight of an FRP cover can also damage the pickup truck box. For example, the unforgiving structure of a heavy weight burden upon the front and sidewall rails of a pickup truck can result in sheet metal deformation and warping. Furthermore, the heavy weight of the cover acts to compress and abrade the gasket materials that provide a water-resistant seal between the cover and the truck bed, which over time results in wear and tear to the paint finish of the pickup truck bed rails. These effects reduce the resale value of the pickup truck vehicle. The inside surface of the FRP cover is usually unfinished and exposes the hand-rolled FRP materials. Cover manufacturers add a secondary painted surface finish or apply a non-woven fabric to hide the rough inside FRP surfaces at extra cost in order to over-come this appearance problem. Finally, in order to adapt the crowned application surface of the FRP cover to the flat rail surfaces of the truck bed, the FRP cover manufacturers use added inserts. This arrangement is typically ineffective because the additional inserts do not adequately compensate for the front-to-back crown along the sidewalls or the side-to-side crowns about the rear and front walls of the FRP cover. Water penetration occurs when a proper seal is not achieved, and water can damage cargo stored in the truck bed. 
     An advanced thermoformed cover substantially overcomes these problems. A thermoformed cover is approximately 35% lighter than an equivalent sized FRP cover, and is easier to remove and re-install at the convenience of the vehicle operator. A lighter weight thermoformed cover decreases long-term fuel consumption and therefore the cost of operating the vehicle. Elements of the second inside sheet of a thermoformed cover can be adapted to conform to the horizontal plane defined by the truck bed rails upon which the cover rests. Therefore, while the first sheet can be crowned to present an attractive appearance and overcome the FRP cover problem of “dishing”, the second sheet can be adapted to provide a uniform compression seal about the truck bed rails which minimizes damage to the painted surfaces. A lighter weight thermoformed cover also produces less deflective forces about the prop mounting points and hinge mechanisms, which in turn reduces the incidence of sheet metal deformation and warping. The inside molded appearance of the thermoformed cover is superior to the rough inside surface appearance of the FRP cover. 
     Another consideration is that roughly 90% of all FRP covers are custom painted to match the color scheme of the pickup truck vehicle. A problem with painted FRP covers is that painting grade gel coat resins have low impact strength, and where the FRP cover edges are exposed and impacted, the painted gel coat chips off the application of FRP paint systems usually includes the use of sensitive activators, agents and solvents that cause worker safety and environmental problems. 
     Another consideration is that FRP covers are difficult to align and install because they are typically poorly executed in design and difficult to handle because of their heavy weight. For example, FRP covers occupy a position above the truck bed rails. The FRP cover includes a foam gasket about its outside margin coexistent with the top of the truck bed rails. This gasket is meant to compress against the rail of the truck bed to prevent water penetration. FRP covers are crowned to reduce the appearance problem of “dishing” at the center. The crown along the front bed wall increases to the middle. If an insert that compensates for this crown in not interposed between the FRP cover crown and the top of the front bed rail, the cover will only restrict water penetration. The FRP cover manufacturers will use an additional combination of strips of the insert material used to reinforce the crown, but this is ineffective because the strips are uniform in thickness and are not crowned themselves. The second sheet of the thermoformed cover can be molded to provide a consistent distance between the inside surfaces of the cover and the outside painted surfaces of the truck bed rails. This arrangement allows the compression points of the thermoformed cover to be evenly distributed and aligned for installation, rather than focused at the crown low points and mal-aligned to the four corners in the case of FRP covers. 
     Another consideration is that when an FRP cover is installed, the FRP cover is usually lifted up by one person standing on the tailgate, and is attached to front wall and the sidewalls by a second or third person. The crown of the FRP cover does not catch on the front wall to prevent the heavy cover from shifting forward against the passenger cabin upon lifting. When the hardware is affixed at a bind, the cover warps or the sheet metal deforms. Elements of the FRP cover do not characteristically protrude below the horizontal plane defined by the top surfaces of the truck bed rails. 
     A characteristic of FRP covers is that the pneumatic props are mounted to the side rail and the cover. This arrangement produces a constant opening force upon the cover when the cover is closed, and in case of heavy-duty FRP covers produces significant focussed prop pressure points. These can deform the sheet metal structures of the truck bed rail when the cover is closed under stress as well as deflect the FRP crown over time. 
     Another consideration is that cover consumers no longer accept vehicle damage, because pickup truck vehicles are becoming increasingly expensive to purchase and operate. FRP cover manufacturers have begun to use fabricated aluminum frames to retain the cover in a position above the truck bed rails. The aluminum rails offer a no-drill installation as well as means for deflecting hinging, prop and cover weight stress upon the painted metal surfaces of the pickup truck vehicle. U.S. Pat. No. 5,688,017 to Bennett is representative of the frame systems used by FRP cover manufacturers. The added economic cost, increased weight and installation difficulties associated with hard cover frame systems is the FRP cover industry&#39;s attempt to correct the damaging effects of FRP cover use 
     Another problem is that there are an increasingly large number of pickup truck types and body styles. An FRP manufacturer must develop a unique lay-up mold in order to produce a cover model for each truck bed size and body style. The consequences of this requirement are varied. When coupled with the paint factor noted above, it can take up to two weeks before a color matched cover can be delivered and installed on the pickup truck for the vehicle owner. The inventory cost to maintain a virtually unlimited selection of color-matched covers in a wide range of truck bed types and body styles is prohibitive. Therefore the cover consumer must be prepared to wait for the manufacturer to produce, paint and deliver an FRP cover to the dealer before the product can be installed onto the vehicle. The FRP cover purchasing process is time-consuming and is not suitable for fulfilling a consumer&#39;s need for immediate gratification. This consequence, plus the high cost of an FRP cover, are the principle factors which have contributed to the increasing popularity of standard black soft covers among pickup truck owners. Accordingly, a need exists for a small number of hard covers that can be adapted to fit a wide variety of truck bed types in the conventional body style sizes. These body style sizes include full-size long and short beds, compact-size long and short beds, intermediate-size long and short beds and full and compact-size sport and flare-side beds. A hard cover of this description would reduce the inventory requirements within the distribution system, and compress the lead-time for delivery. This type of hard cover would also provide a more robust and tamper proof product than a soft cover which can be slashed open with a knife by vandals and thieves. 
     Another problem with conventional FRP covers is that they use opposed pneumatic props to support the cover in an open position. The disadvantage of this arrangement is that access to the cargo area of the pickup truck bed is restricted from the sides by the props. 
     SUMMARY OF THE INVENTIONS 
     It is a primary objective of the present invention to provide a rigid cover for a pickup truck bed in order to protect cargo and property against weather and from vandalism. 
     Another objective is to provide a cover comprised of two sheets of thermoformed plastic, which offers several economic advantages. Thermoforming offers clear production volume advantages, which will permit the more advanced product to be distributed into a wider market territory. Thermoforming is lower cost and will allow the consumer to benefit through lower pricing. Thermoforming poses less risk to worker safety because the process does not release harmful emissions and violates. Thermoforming materials are sensitive to the environment and are 100% recyclable. 
     Another objective is provide a cover that offers several consumer friendly benefits. A lighter weight thermoformed cover is more user friendly allowing the vehicle operator to install and remove the cover with greater ease. A lighter weight cover consumes less fuel to reduce vehicle-operating costs over time. 
     Another objective is to use a processing technology and materials that are safer for the environment and have less worker safety issues. 
     Another objective is to produce a cover with a full perimeter watertight seal to prevent cargo damage and paint abrasion. 
     Another objective is to encapsulate the cover hardware between the two sheets of the cover to provide a more attractive appearance and finish. 
     Another objective is to add front retaining wall to the inside sheet of molded plastic to aid in the installation and removal of the cover from the truck bed. A feature that can be added includes an alignment guide for installation. 
     Another objective orientates the cover lifting springs to produce a constant closing force, which reduces deflection of the cover and compensates for elevated temperature conditions that may cause the cover to deflect. 
     Another objective adapts the cover to use coil springs operable from the front of the cover in substitution of opposed pneumatic props that restrict access to the truck bed from the sides. The objective provides springs, which do not interfere with the installation of other truck bed accessories. 
     Another objective adds load bearing and shape retaining strength to the second inside sheet of thermoformed plastic with the addition of molded in reinforcing elements. The individual reinforcing elements may themselves include stress reducing features comprising notches and interconnecting bridges, and are preferably arranged in patterns that impart additional front-to-back and side-to-side cover crown strength while deflecting localized hinging and focussed pressure stress points. 
     Another objective increases strength to the cover where the cover&#39;s crowned top surface transitions into the down-turned cover walls that define a perimeter lip. A hollow area along the linearly extending transition is provided between the two sheets forming the cover to increase load-bearing strength. 
     Another objective inserts load-bearing and cover shape retaining members between the two sheets comprising the cover, which members enable the cover to be constructed in thinner gauge sheets that improve strength-to-weight and cost/price ratios. 
     It is still yet another set of objectives to produce a cover that is adaptable to a wide range of truck beds within certain truck bed size categories. 
     Additional objectives therefore include providing a cover assembly product line comprising a small number of covers in common sizes, and a large number of rail adapter kits that are specific to each make and model of truck bed in the common sizes. The cover component of the assembly incorporates the cover features listed above in connection with the improvements over conventional FRP style thermoformed covers. The rail components themselves include other features. 
     Another objective is provide a four part rail kit, comprising one front wall and two side wall components operable to engage the truck bed rail and a rear wall component operable to engage the rear wall of the cover component. This arrangement produces a full perimeter boarder appearance and operates to restrict the tailgate from being opened without first opening the cover. The tailgate is maintained in the dosed position under lock and key by the cover to prevent theft and vandalism. In alternate arrangements, the rear wall component of the rail kit is operable for mounting upon the tailgate, but this arrangement is not always preferred because tailgates are not amenable for clamps or no-drill installation. 
     Another objective is provide front and side wall rail components with a channel to receive the down-turned walls of the common sized cover. The position of the channels on the truck bed adapting rail components is pre-determined by the relative position of the perimeter margin of the cover component. The channel includes draining features and may be reinforced to add strength to rail components and prevent paint abrasion of the truck bed. 
     The rails include details that are further operable to enclose clamps that attach the rail components to the truck bed rails for appearance purposes and a no-drill installation. The front rail channel includes an angled portion designed to receive the pivoting front wall of the cover. The rail components may be constructed out of a single sheet or a plurality of sheets molded and bonded together for hardware supporting and cover bearing strength. 
     Briefly, in accordance with this invention, there is provided a twin-sheet cover for installation onto the bed rails of a pickup truck. The cover, including hardware may be operable with the truck bed alone, or in cooperation with rail adapting kits. 
     Other objects and advantages of the present embodiments will become apparent from the following descriptions and appended claims when taken in conjunction with the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the prior art positioned upon a pickup truck bed. 
     FIG. 2 is a partial perspective view of the present invention in an open position upon a truck bed. 
     FIG. 3 is a cross section of the prior art taken along line A—A of FIG.  1 . 
     FIG. 4 is a cross section of the one embodiment of the present invention taken along line B—B of FIG.  2 . 
     FIG. 5 is an exploded sectional view of the sidewall region of the prior art. 
     FIG. 6 is a plan view of the footprint of communication between the prior art and a truck bed. 
     FIG. 7 is a plan view of the footprint of communication between the present invention and a truck bed. 
     FIG. 8 is a section showing the front wall of the prior art. 
     FIG. 9 is an elevational view the front wall of FIG.  8 . 
     FIG. 10 is a section view showing the prior art at the center location shown in FIG.  9 . 
     FIG. 11 is a section showing the present art along the front wall. 
     FIG. 12 is a side elevation view of the present invention in front of the front truck bed wall. 
     FIG. 13 is an exploded view of the prior art supporting means for spring props. 
     FIG. 14 is a side elevation view suggesting the open and close forces associated with the props. 
     FIG. 15 is an exploded view of the present invention showing the preferred prop support arrangement. 
     FIG. 16 is a side elevation suggesting the props provide a constant closing force when closed. 
     FIG. 17 is a plan view of the inside or second sheet of the present invention. 
     FIG. 18 is an exploded view of the mold adaptation to accept a reinforcing insert. 
     FIG. 19 is a section of the present cover reinforced with an insert. 
     FIG. 20 is an exploded view of the present invention coupled with another present invention over the bed of a pickup truck. 
     FIG. 21 is a sectional view showing the interface between the hard cover and the molded platform protecting the truck bed along the sidewalls. 
     FIG. 22 is a sectional view showing one possible interface between the hard cover and the molded platform along the tailgate. 
     FIG. 23 is a sectional view showing an interface between the hard cover and the molded platform along the tailgate. 
     FIG. 24 is a sectional view showing one possible interface between the hard cover and the molded platform along the tailgate. 
     FIG. 25 is a sectional view showing one possible interface between the hard cover and the molded platform along the tailgate. 
     FIG. 26 is a plan view showing the overlying dimensions of a plurality of trucks in the standard full —size short bed model range, and the relationship of the hard cover lip to that overlying dimension. 
     FIG. 27 is a sectional view showing the molded platform and hard cover in a closed position along the front wall. 
     FIG. 28 is a sectional view of one embodiment of a side rail member. 
     FIG. 29 is a sectional view of another embodiment of a side rail member comprising a C channel and an adjustable tie-down hook. 
     FIG. 30 is a sectional view of one embodiment of a prop support showing a double sided C channel with adjustable ball studs and tie-down hook. 
     FIG. 31 is a perspective view of a load-bearing member that may be attached to the cover. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, there is seen a perspective view of pickup truck vehicle  2  showing a one piece rigid FRP cover  4  custom painted to match the color of the truck  2 . The cover  4  includes a crowned top surface  6 , opposed down-ward extending side walls  8 , and a down-ward extending front wall  10  and rear wall  12 . A T-handle lock  14  is shown affixed to the rear wall  12  of FRP cover  4 . The cover  4  is representative of all FRP covers sold into the market. 
     Referring now to FIG. 2, there is seen a perspective view of one embodiment of the present invention in an open position on a truck bed  3  comprising opposed side walls  5 , front wall  17  and tail gate  9 . Thermoformed cover assembly  16  comprises crowned cover  15  that includes downward extending walls  18 , and a molded platform  23 . Molded platform  23  comprises a bed rail adapter kit  20  including opposed bed rail adapters  21  which coexist and substantially conform in detail to the truck bed rails  22 , such that there is substantially no gap between the outside and inside vertical surfaces of the bed rail adapter kit  20  and the truck bed rails  22 . This arrangement provides an attractive appearance as well as resistance to water penetration. 
     Cover  16  comprises a first thermoformed sheet of plastic  24 , hereinafter referred to as top sheet  26  and second thermoformed sheet of plastic  28 , hereinafter referred to as inside sheet  30 . As can be seen, inside sheet  30  includes a plurality of embosses  32 , which embosses  32  are adapted to impart load-bearing strength, encapsulate hardware, and provide other functional features that will be described below. Opposed side rail adapters  21 , tail gate rail adapter  34  and front wall rail adapter  35  are included in rail kit  20 . Also seen are opposed pneumatic props  36 . 
     Referring now to FIG. 3, a cross section of FRP cover  4 , taken along the lines A—A in FIG. 1, is seen. FRP cover  4  includes a top surface  38  comprising a painted gel-coat finish  40 , a first layer of lay-up fiberglass  42 , a cover reinforcing member  44 , (paper honeycomb shown) and a second layer of lay-up fiberglass  46 . Cover  4  also includes rail insert members  48  which are inserted between FRP layers  42  and  46  to compensate for the front to back crown of cover  4  so that the bulb gasket  50  compresses against the top  52  of the truck bed rail  54 . As is illustrated to advantage, member  48 , which comprises two strips of member  44  material, does not do a very good job at compensating for the crown because it is a substantially flat construction. Accordingly, water and road debris may penetrate the cargo compartment  56  through gaps existing between the truck bed rail  54  and the sidewalls  8  of cover  4  in the area taken along lines A—A. 
     Referring now to FIG. 4, a cross section of a thermoformed cover  60  is shown. Cover  60  comprises top sheet  26  and inside sheet  30 . Top sheet  26  and inside sheet  30  are permanently joined in a plurality of twin-sheet locations  62 . Inside sheet  30  comprises a plurality of depending portions  64  that do contact the top sheet  26 . Each portions  64  serves a purpose. One purpose of depending portions  64   a  is to provide load-bearing strength in areas of weakness  66 . These include the center area  66   a  of the cover, which are reinforced by groupings of molded in shapes  69  that impart load-bearing strength and are off-set to prevent hinging action along lines or points of stress. More on these details later. Portions  64   b  (seen in FIG. 17) are also used to encapsulate hardware for hinges  80 , props  86  and the like  102  as well as single and multiple point locking mechanisms  14 . Portions  64   c,  comprising perimeter ledge  65 , are provided to create a bulb gasket  68  gluing surface  51  which is substantially co-determined by the top surface  52  of bed rail  54 , the diameter and durometer of gasket  50  and the weight of the cover  60 . Portions  64   c  include gasket  68  that compress against the top surface  52  of all truck bed walls  5 ,  7  and  9 . Portion  64   d  is adapted to provide strength along the front to back and side to side areas where the walls  8 ,  10  and  12  transition into the crowned top surface  6  of cover  60 . 
     As can be seen in FIG. 3, gasket  50  is not in full contact or compression against the truck bed rails  54 . This arrangement results in cover  4  mal alignment and potential rubbing of the walls  8 ,  10  and  12  against the truck bed surfaces  70 . In order to overcome this potential problem, FRP cover  4  manufacturers have introduced fabricated aluminum rail kits  74 . FIGS. 5 serves to illustrate this approach generally, as there are several patent pending variations of kit  74 . Aluminum rail kit  74  comprises uses “C” channel  78 . The “C” channel  78  is used for several purposes. Adjustable standoffs  76  are positioned in channel  78  to prevent cover  4  from compressing against the rear of the truck bed rails  54  as a result of the condition characterized in FIG.  3 . Channel  78  also supports hardware to locate fixed lock keeper  80 , which lock keeper holds the cover above the rail  54  to prevent abrasion caused by mal-aligned cover  4 . Standoff  76  and keeper  80  are used in cooperation to retain cover  4  above bed rails  54 . This arrangement does not compensate for the front to back, or side to side crown of cover  4 . Therefore as FIG. 5 shows, water is still able to penetrate the cargo compartment  56  between the gasket  50  applied to the cover  4 . Channel  78  is also used to hold prop bracket  88  and front hinge bracket  89 . 
     Now referring to FIGS. 6 and 7 FIG. 6 shows the foot print  91   a  of FRP cover  4  in the areas where the gasket  50  compresses against the bed rail  52  to provide a water tight seal. The areas of improper or no seal are caused by the uncompensated for distance that the crown extends above the truck bed rails  54  along the margin connecting the walls  8 ,  10  and  12  to top surface  6 . FIG. 7 shows how the perimeter ledge  65  of portion  64   c  of inside sheet  30  compensates for the front to back and side to side crowns to provide a predetermined space between the cover  60  and the bed rails  52 . This arrangement increases the seal area to prevent water and debris penetration, while also equally distributing the load of the cover  60  upon the bed rails  52 , which reduces abrasion and deformation along the hardware points associated with portions  64   c.  The footprint  91   b  of cover  60  shown in FIG. 7 corresponds to gasket  68 . 
     Referring now to FIGS. 8,  9  and  10 , a section of cover  4  is shown in FIG. 8 in the area of the front wall  7 , where the FRP cover  4  is mounted to the wall  17  by hinge  79 . Gasket  50  is 
     Referring now to FIGS. 8,  9  and  10 , a section of cover  4  is shown in FIG. 8 in the area of the front wall  7 , where the FRP cover  4  is mounted to the wall  17  by hinge  79 . Gasket  50  is provided as a seal to compress along the front wall  10 . As can be appreciated in connection with FIG. 9, rail insert  48  is provided to adapt cover  4  to front wall  17  of truck bed for gasket  50  and added strength for hinge  79 . Where cover front wall  10  extends up to meet crowned cover  6 , rail insert  48  is raised above front rail to a position where gasket  50  does not communicate with bed rail  52 . This relationship is suggested by distance X at the center and distances Z at the sidewalls  5 . As shown in FIG. 10, taken at a position in the center of the cover  4 , this arrangement creates a non-sealing zone that permits water and debris to enter the cargo compartment of the truck bed  56 . The same condition is duplicated along the tailgate  9  of the pickup truck  2 . It should be noted that cover  4  can be adapted so that piano style hinge  79  attaches to the bottom terminus  81  of front wall  10  to provide a better sealing (and hinging) condition for certain cover  4  brands. 
     Referring now to FIG. 11, showing thermoformed cover  60  in the same area as seen in FIG. 10, second sheet  30  includes portion  64   c,  which compensates for the crowned cover  6 . Also seen is portion  64   e  extending downward in a position contiguous to front bed rail  17 . Contiguous to portion  64   c  is channel  65 , which channel  65  may be adapted to receive hinge  79  or elements thereof. Portion  64   e  of second sheet  30  is provided to prevent cover  60  from shifting forward when cover  60  is lifted at wall  12  so that the cover  60  can be engaged to hinges  79  from the side wall  5  of the truck bed by a first or second person. Portion  64   e  also operates to insure that the cover  60  is property aligned to the front wall  17  at the time of first assembly and installation of cover  60  to truck bed rails  54 . (A tape with a side to side center mark may be temporarily applied to front rail  17  for this purpose.) The depth of down-ward extending portion  64   e  may also be interrupted by sub-portion  64   ee  having guiding mark  82  molded or applied to cover  60 , which mark  82  may be used to align cover along center line of truck bed rails  54 . This relationship is shown in FIG. 12, which is a view from inside the bed  56  looking toward the front wall  17 . 
     Referring now to FIGS. 13 and 14, FIG. 13 shows the relationship of the pneumatic props  86  to the operation of cover  4 . A first ball joint  88  is attached to the rails  54  directly, or by way of rail kit  74 , as shown. A second ball joint  90  is attached to cover  4  in approximate lateral alignment with first ball joint  88 . Pneumatic prop  86  is attached to ball joints  88  and  90  such that rod end  92  is attached to ball joint  88 . In this arrangement, shown to better advantage is FIG. 14, prop  86  provides a constant opening force when cover  4  is closed, suggested in phantom. 
     As seen in FIGS. 15 and 16, another arrangement is preferred for cover  60 . Inside sheet  30  includes opposed portions  64   f  comprising opposed prop supports  94 . Prop supports  94  includes spaces  96  for prop reinforcement blocks  98  for mounting ball studs  90 . Prop supports  94  preferably extend below the sidewall  8  as shown. Supports  94  may also terminate before extending beyond the margin of wall  8  for packaging purposes. This arrangement is preferred because the rod end  92  produces a constant closing pressure or downward projecting force when the cover  60  is closed. As cover  60  is closed, rod end  92  compresses to its fullest extent before reaching the closed position. As rod end  92  extends past 90 degrees or 100% compression from fixed ball stud  88 , rod end  92  extends upon completely closing to produce downward pressing force. This force is preferred for thermoformed cover  60  because cover  60  has less high temperature strength than FRP cover  4 , and is seen to better advantage in FIG. 16, with the props  86  shown in phantom in the closed position. The downward extending props  89  push the cover  60  into the closed position to seal cover  60  to truck bed rails  54 . This arrangement also has a tendency to pull the cover  60  side walls  8  into the bed rails  54 , rather away from the bed rails  54 , as is the case in FIG. 14 when cover  4  is closed. 
     In order to optimize (reduce) the thickness of sheets  26  and  30 , another arrangement for supports  94  is preferred. When the cover  60  is closed, a moment of stress is created which can cause the edge of supports  93  toward the center of gravity to deflect before the props  92  begin to compress. The support  94  can therefore be extended in front to back length to assist in deflecting the moment of stress away from the focussed area associated with the embodiment shown in FIG.  17 . The desired length of long support  95  exceeds the full extend length of props  92 , so that the moments of closing and opening stress are distributed over increased areas of cover  60 . 
     As seen best in FIG. 17, sheet  30  is molded with both embodiments of supports  94  and  95 . Support  95  may be further adapted to include one or two channels  97  and  99 . Channel  97  would be for the ball stud  90 . The channel  99  would be for accessories and load bearing members  103 . The insert  98  would be substituted for a double-sided C channel  101 . The additional advantages of channel  97  include being able to shift the ball stud  90  to increase or decrease the operating strength of props  92 . This arrangement compensates for the additional weight of channel  99  accessories. Such accessories would be load bearing cross member assemblies  103  adapted for carrying fishing poles, paddles, garden equipment, as well as many other types of cargo. The side rail detail  176  may be lengthened front to back to allow for ball stud  88  repositioning of prop  86  arrangement in embodiment  160  of FIG.  20 . 
     Another arrangement preferred over that described in conjunction with FIGS. 15 and 16 is formed wire spring  100 . Spring  100  comprises element  102  adapted to engage the front wall  17  of the truck bed and element  104  adapted to engage the inside sheet  30  of cover  60 . Element  102  preferably resides against front wall  17  and extends to an operable position below the truck bed rails  54  so that spring  100  does not interfere with other truck bed accessories. Element  104  extends front to back along inside sheet  30  and may be encapsulated between sheets  26  and  30 . Interposed between sheets  26  and  30  along the extended length of element  104  may be reinforcing elements (not shown), which elements are adapted to deflect pressure of spring  100  over wide area of cover  60 . The coil  106  of spring  100  is positioned in alignment with the pivot motion of hinge  79  along the front wall  17  of bed rail  54 . Other spring mechanisms may be substituted for formed wire spring  100 . An advantage of this arrangement, which is shown in phantom in FIG. 16, is that it does not restrict access to the cargo area of the truck bed from the side of the vehicle. This arrangement also has the beneficial effect of the element  104  supporting the crown  6  of cover  60 . 
     Portion  64   e  of inside sheet  30  is further adapted to allow cover  60  to be pre-positioned against front wall rail  54  so that spring  100  can be engaged for a no-drill application. A keeper  108  (not shown) may be used to retain the spring  100  in a position adapted for easy installation. The lock assembly  14  retains cover  60  in a closed position. Formed wire spring  100  may also be substituted with other styles of spring keeping in mind the advantages outlined above. 
     Also seen in FIG. 15 is portion  64   d  of inside sheet  30  that is provided to add strength to the cover  60 . Portion  64   d  may comprise a single hollow section  110  running the length of the cover  60 , or a plurality of hollow sections  110  running the length of cover  60 . The portion  64   d  adds strength by creating tubular and/or bridging effects that provide lateral anti-twisting strength as well as wall  8  strength. Portion  64   f  may also include opposed elements  112  which align with the truck bed rail  54  to prevent the cover from shifting side to side to ease installation and to prevent vandalism to cover  60 . 
     Referring now to FIG. 17, a plan view of inside sheet  30  is shown. Within the border defined by the gasket  68  which corresponds to the bed rails  52 , it may be understood that portions  64   a  comprise a plurality of oblong and triangular patterns  114  that extend below the mating surfaces  62  between sheets  26  and  30 . The patterns  114  provide localized strength individually as well as generally in conjunction with other patterns  114 . For example, patterns  114  designated  114   a, b  and  c  are arranged to produce the configuration of a triangle which imparts load-bearing strength to sheet  30 . A triangle configuration that is positioned to provide support at the center of gravity  124  of cover  60  is preferred. As indicated by pattern  114   d,  in phantom, the patterns  114  may also be adapted so that center portions  116  are removed to provide additional load bearing strength in the unsupported areas of patterns  114  between sheets  26  and  30 . Furthermore, patterns  114  may be arranged in configuration to reduce the incidence of hinging between the lateral lines of stress created between each pattern  114 . Pattern  114   c  is positioned so that dotted line  118  intersects with pattern  114   e  to prevent a hinging area. Areas between patterns  114  may also be interconnected with bridges  120  to prevent hinging. “V” grooves  122  may also be used to break up the lateral stresses that may occur when the cover  60  is subjected to resistance associated with compressing props  86  or springs  100 , as well as other load producing effects. 
     As may also be seen in FIG. 17, inside sheet  30  may also include lock assembly housing  64   g  that encapsulate two-point lock assembly  126  (not seen here) comprising a center mounted t-handle  128  or the like, and opposed lock rods  130   a  and  b,  or the like. (Rod  130   a  is shown in the extended position, and Rod  130   b  is shown in the retracted position.) 
     In order to maximize the load bearing strength of cover  60  while using thinner or light weight sheets  26  and  30 , it is preferred to provide strengthening inserts that can distribute the stresses that will flex the cover  60 . Two such methods are contemplated. In reference to FIG. 15, a length of angle  132 , or the like, may be installed in elements  112  of inside sheet  30  to provide load bearing strength as well as deflect the focused pressure points upon crown  6  associated with the operation of props  86 . Alternatively, as shown in connection with FIGS. 18 and 19, reinforcing member  134  may be inserted onto blocks  138  on mold surface  136  before inside sheet  30  is thermoformed. When sheet  30  is draped over member  134  and thermoformed, elements of sheet  30  on passenger side  140  of member  134  will knit with elements of sheet  30  on driver side  142  in the notched areas  144  and along the gap  150  provided by the step  146  of blocks  138 . After sheet  30  is molded over member  134 , member  134  will lift away from molding surface  136  and be encapsulated within sheet  30  to impart a great deal of load bearing strength. This relationship is illustrated to advantage in FIG.  19 . Member  134  is preferably constructed of the same plastic material as sheet  30  so that hot tack adhesion occurs between the sheet  30  and member  134  when sheet  30  is being thermoformed at an elevated temperature. The advantage of this arrangement is that cover  60  will remain 100% recyclable. Member(s)  136  may be adapted to run front to back and/or side to side to increase the load bearing strength of cover  60 . Members  134  may also be adapted to intersect patterns  114 . 
     It should be understood that manufacturers of FRP covers  4  have to make a dedicated mold for each truck bed model offered in the markets serviced in order to fill demand. At any point in time, this means that the manufacturer must have literally dozens of dedicated molds and several new molds under development for new model introductions. It would not be uncommon for a full-line manufacturer of FRP covers  4  to have a model selection of 50 too 100 separate and unique tonneau cover  4  models. Therefore, the need exists to develop what might be referred to as a universal product line, which line comprising 8-9 models is adaptable for all truck bed makes and models sold into the North American market. As seen in FIG. 20, cover assembly  160  is contemplated for this purpose. 
     Cover assembly  160  comprises thermoformed cover  162  and adapter rail kit  164 . In the proposed universal product line, there would be 8-9 cover  162  models, and a larger number of rail kits  164 . The cover  162  and rail kits  164  would be sold in separately packaged containers, so that distribution inventory requirements would be kept to a minimum. As may be appreciated, an inventory of 8-9 cover  162  models and the most popular selling rail kits  164  would be considerably less costly and take less inventory space than maintaining an inventory of 50 plus FRP cover  4  models. Indeed, the lower inventory requirements of the proposed cover assembly  160  would enable light truck accessory merchants that are currently outside the cover  4  market to offer the consumer cover  160  at a lower price, with faster delivery, and do-it-yourself installation. The present cover  160  would have the effect of increasing the variety and purchasing convenience for the consumer. 
     FIG. 26 suggests a plan view of the bed rails  54   a, b  and  c  of the top selling domestic pickup trucks with downsize truck beds. The overlapping area  166   a  of the plan view is suggested in the exploded sectional view of  166   b.  The downward extending walls  8 ,  10  and  12  of cover  162  are adapted to terminate within zone  167 . The rail kits  164  are adapted to fit the bed rails  54  specific to each truck bed model, and include rail kit channel  168  to receive the downward extending walls  8 ,  10  and  12  of cover  162 . The channel  168  is positioned on each rail kit  164  to receive cover  162  in the area corresponding to zone  167 . 
     This arrangement is best illustrated in FIG. 21, which shows cover assembly  160  for a truck bed model that includes a factory installed plastic bed rail cover  170 . The cover  162  has opposed downward extending sidewalls  8  and a gasket  68  for sealing within channel  168 . Rail kits  164  are adapted to install upon bed rails  54  by a plurality of clamps  172 . Where the inside downturn lip  174  corresponds to position of clamp  172 , lip  174  is adapted to include projections  176  to cover clamp  172  for appearance purposes. Projections  176  may be further adapted to receive hardware for lock assembly, hinge assembly and prop assembly. Rail kits  164  may also be secured to bed rails  54  by double-sided tape  178 , or prevented from abrading the paint of the bed rails  54  by single-sided tape  180 . Rail kit  164  channel  168  can be developed to reside on a plane above or in contact with bed rails  54 . The advantage of channel  168  residing above the bed rails  54  is prevention of abrading the paint off. The advantage of contacting the rails  54  is for added load bearing support and anti-flexing of cover assembly  160 . Channel  168  may be further adapted to receive a drain opening  182  and a series of depressions  184 , which depressions are adapted to extend downward from channel  168  to meet bed rails  54  as added means for achieving rail kit  164  load bearing support. The rail kit  164  may also be constructed from two sheets of molded plastic, such that inside sheet (not shown) offers the support provided by depressions  184  and the draining operation of opening  182 . 
     Rails kits  164  may also comprise two plastic members  165  and  167 . As seen in FIG. 28, rail kit element  174  (shown in phantom) of member  165  may be adapted to receive a C channel  175  for laterally adjustable tie down hooks  177  and the like. The C channel  175  is preferably encased between members  165  and  167 . Clamp  172  may be adapted to engage channel  175 . Other hardware may be adapted to engage channel  175  at the hinge and locking mechanisms as well. 
     Cover assembly  160  requires further adaptation in the area of the tailgate. As seen in FIGS. 24 and 25, overlapping zone  167  at the tailgate  9  is narrow along the side to side path, such that it is advantageous to provide a tailgate rail kit member  186  that attaches to the cover  162  rather than the tailgate bed rail  54 , as seen in FIG.  20 . This arrangement has several advantages. First, if the member  186  is attached to the cover  162 , the member  186  operates to keep the tailgate from being opened by thieves or vandals. Second, it is advantageous to provide a no-drill cover assembly  160 . Tailgates are not adapted to receive clamps  172  and therefore a tailgate-mounted member  188  would have to be mechanically fastened to the tailgate. It is contemplated that member  186  would be fastened to cover  162  mechanically, by adhesives or the like, and would comprise one or more separately thermoformed parts  190  and  192  bonded together. The outside part  190  would be adapted to blend in with the contours of the side rail kit members  194 R and  194 L for cosmetic reasons. The inside part  192  would be adapted for mating to the cover  162  as well as providing a seal against the tailgate  54 . The inside part may include depression  194  to receive gasket  68 . These tailgate arrangements are seen in FIGS. 22,  23 ,  24  and  25 . 
     Refering now to FIG. [ 27 , the front wall  10  of cover assembly  160  comprises crown cover  162  and front wall rail kit member  196 . The front wall  10  of cover  162  resides in front channel  169  of member  196 . Member  196  includes thermoformed plastic components  198  and  200 , that are glued together. Member  196  is adapted with means for hinging, means for removing the cover  162  from rail kit  164  and means for no-drill installation. Optionally, member  196  may be adapted to receive formed wire spring  100  or the like as well. Channel  169  includes a substantially horizontal surface  202 , which receives compression gasket  168 , a channel base surface  204  and an angled outside surface  206 . Surface  206  angles a predetermined amount corresponding to the arc of swing traveled by cover  162  from the closed position to the open position. It is understood that cover assembly may be adapted in other manners to allow front wall  10  of cover  162  to travel within channel  169  for opening and closing. 
     The front wall hinges (not shown) of covers in preferred embodiments may also be adapted to include a lockable hinge release mechanism  208  for easy removal of covers  60  and  162  from the truck bed. Hinge mechanism  208  includes side accessibility operatable to lock the hinges in open and closed position for safety and security. The body of hinge release mechanism would be housed within portions  64  of sheet  26  and  30 . The hinge area  210  of sheet  30  and corresponding rail kit member  196  may be adapted to receive releaseable hinge(s)  212  or wire spring  100 . 
     Briefly, in accordance with this invention, there is provided a twin-sheet cover for installation onto the bed rails of a pickup truck. The cover, including hardware may be operable with the truck bed alone, or in cooperation with rail adapting kits. It is to be understood that the drawings and descriptive matter are in all cases to be interpreted as merely illustrative of principles, methods and apparatus of the invention, rather than as limiting the same in any way, since it is contemplated that various changes may be made in various elements to achieve like results without departing from the spirit of the invention or the scope of the appended claims.