Paul, I built your truck camper, and am ridiculously self-satisfied with the result. Your plans were well-written, easy to follow and presented the project such that an amateur like me had little trouble completing it. Many thanks for putting this out there.
My unit was sized to fit within a new Dodge Ram with a 6' 4" box. It weighs in at 640 lbs. with a teardrop camper door, RV window, 14 inch variable speed ceiling fan, an inteli-power converter and LED lights. As you suggested, I covered everything in six ounce cloth and numerous coats of tinted epoxy. I built it over a three month period, devoting about 35 days to the project. I recessed the access door to allow the truck gate to close tightly against the back (the hinges protrude about 3/4 of an inch).
Four strong friends were adequate to load it, though I've now purchased two cable jacks so that I can put it on and off myself. I reinforced the four corners during construction to add hard points for securing it to the stock cleats inside the bed of the truck. The system for making it secure took a little thinking, and a combination of ratchet straps and turnbuckles proved to work well. I took photo's during most of the construction phase and will happily share them with anyone who wants. I've included a few with this email.
I've just returned from a three week trip to the Yukon where this thing proved extremely efficient. The truck barely knows it's there while driving (though the flat front of the camper where it protrudes over the cab collects a fair number of squashed bugs). Two removable inserts make for comfortable beds. I still need to add the canoe rack, which I'll put on this fall. Once again, many thanks for this. Great design.