I built this cap from Owens Corning FOAMULAR XPS. Covered inside and out with PMF (poor mans fiberglass), painted glued canvas. I made two rear panels, one with a door and window the other as a clamshell style hatch. It's light weight and has a removable bunk inside and a roof fan. Cost to build $2k. Weighs 120 lbs. with the clamshell hatch and 210 lbs. with the window/door panel and bunk installed. Truck caps are hard to keep dust out when driving on dirt roads so the door/window rear panel on the bed is sealed all the way around to keep the dust out. I've driven this over 500 miles with 60 miles on washboard roads and on the highway up to 75 mph. I made a test piece, two pieces of the foam glued together at 90°, with painted canvas which has been sitting out in the elements for 6 months now and hasn't had any delamination. I got this idea off a facebook group called foamie campers and trailers, where members are building teardrop camp trailers.
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