The back panel is a finely woven breathable mesh. The rest of the pack is 1000 denier mesh except for the bottom panel, side wings and top storm flap made of 200 denier ripstop nylon. The sternum strap is fully adjustable and removable. Lifter straps pull the load forward over the shoulder. Plastic loop-locs allow for use of the standard hip belt if so desired.
Tarps just make sense.
For starters, they avoid unnecessary features like floors and doors. A door can be fashioned from garbage bags fastened to the strategically placed ties. Tarps are easy to set up and tear down. Last but not least, there's no condensation problem. If you're the creative type, you can rig the tarp in shapes other than the basic A-frame design.