Can't wait to see what you come up with for those doors. I have some bolts that just refuse to come out. Not sure if uhaul used some type of impervious locking compound. I must have dropped 40lbs. of dirt, and rust when I removed my box.
Got a younger fella here that has a CAD run aluminum plasma cutter etc at his shop. I'm going to yank the old doors right off and He's going to weld in 1" aluminum tubing in the back where the doors went. He also does colored aluminum skin like cargo trailers. It will be glued and riveted to the tubing. The old hinge supports on the box will be used as partial support for the ladder, spare tire/roof rack that will fit in there. Going to tie it to a nice 8' X 6' roof top carrier. Did you do any extra reinforcing to the under frame? I am missing a few of the angle iron cross pieces that came out from the frame and were mounted through the floor with counter sunk bolts. Those will get replaced next. Going to wire wheel the box frame and paint it. Sand blast and paint the truck frame.