After much deliberation and drawing, I think I've come up with a idea. Instead of having to buy windows and doors, I found an old camper shell that fit a 6'6" truck bed. It already has sliding windows on the side and a hatch in the back that will make a great door. I'm using 3/4" treated plywood for the side walls and sleep floor. On the bottom of the trailer I've made two compartments that are approx. 24" tall and 30" wide for storing totes full of supplies. Above that area will be the sleeping area. It has approx. 40" of height so I can sit up and not hit the top, with room to spare.