I did mine a little diffrently, I did not support the doors, would have been a good idea but i had no problems without doing so. I used a fork lift to lift the body from behind. The fork lift had a single long boom about 10' long. I set this over the tub from the back all the way to about the windshield, I then used chains up and over the boom to bolts put through each body mount(three chains.)
This held the tub flat without braces. I then set the tub down on eight stands made from disc blades 1 1/4" pipe with a piece of 3/4" pipe sleeved inside to make the hieght adjustable by drilling a hole in the side and welding a nut on to place a bolt in to tighten. The stands sat under each of the eight body mounts, I dropped a bolt through the body mount and into the pipe to help secure things.. When I media blasted the tub I held it up by the fork lift to do th eunderside and when I painted it it was on the stands about 4' up so I could get under it to paint.
Sorry no pictures the media card in my camera during the whole frame off was stolen/lost before uploading to computer. This system worked ok, it allowed me to do everthing by myself, if all the stands were bult on one big rolling cart it would have been easier to move but i only moved it 3 times and I had the luxury of a fork lift. I also didn't have to replace any floor boards, I did one rocker before removing it from the frame. I was fortunate to find a rust free 69.