I'm thinking about chopping the top off of my spare camper top so only the bottom frame, front (with sliding glass window), sides (minus the sliding glass windows), and a little bit of the top are left. I can then build up dual layers of coroplast on the sides and git the correct slope angle to the rear. This platform should allow me to adjust the slope angle just by chopping the sides down. I can always put in windows as I progress...
The rear hatch will not have a window in it while I test. I'll eventually have to git a rear camera system installed so I won't be totally blind back there.