1.  Field of the Invention
This invention relates to containers of the kind having a base with a load-carrying surface and a cover which is sealed to the base by an inflatable tubular sealing member.  Typically the base has an impermeable load-carrying surface, and the cover is a flexible impermeable envelope to cover goods on said base, which envelope is sealed to the base by an inflatable tubular sealing member extending around the periphery of the envelope to hold the envelope in airtight sealing engagement against a part of the base assembly. 
2.  Prior Art
Containers of this kind are used by putting the envelope of impermeable material over a load on the air-impermeable base and then sealing the periphery of the envelope to the base by an airtight seal; the space within the envelope may then be partially evacuated so that the reduced pressure holds the envelope tightly down onto the base; if the envelope is flexible it is drawn down onto the load and so holds the load firmly onto the base.  In some cases the region inside the envelope may be pressurised, e.g. with dry air or an inert gas.  Such packaging systems find particular application for loads which may have to be transported but which may also have to be stored for long periods.  By evacuation, the envelope provides the required restraint on goods during transport and also serves to protect the goods during storage.  Both for transport and for storage, it is necessary that the envelope should be sealed to the base in an airtight manner.  For this purpose, it is known to use an inflatable tubular seal.  Such a seal may be formed as a tube integral with or secured to the periphery of the envelope as described for example in U.S. Pat.  No.  3,850,214 or it may be a separate tube either fitting in or secured to the base (see for example British Pat.  No.  860,238).  Very conveniently the periphery of the envelope is put within a slot or groove extending around the base and the aforementioned tube inflated to seal the periphery of the envelope against one or both walls of the slot or groove.  For example, the tube may be placed within the slot or groove and the periphery of the envelope then put within the slot or groove between the tube and one side wall of the slot or groove; the tube is then inflated to press the envelope against that side wall. 
It has been found that, particularly with long-term storage, there may be leakage from the tubular seal, for example a slow leak through the inflation valve, so that, after a long term, the tube has lost so much pressure that the seal is no longer airtight.