I've never pulled the floor completely out of one so I'm not an expert, but many of the older campers rested on jacks that were fastened under the wings of the tub. Electric corner jacks were a luxury. 2x supports under the wings in addition to the corner jacks will support it while you remove the floor.
You said that you were concerned that the sides may spread once the floor is removed. I used 2 Erwin 50" hand clamps a couple of weeks ago to pull the tub walls together while removing the cross braces to have them re-welded. Since your jacks are on the corners and you aren't working with a rot condition, the end walls should hold it together.
You mentioned beefing up the floor. In addition to increasing the truss thickness a little and using only plywood(no particle board), something I really like for additional strength at very little cost or weight, put in structural foam board between your truss members and bond both sides with polyurethane adhesive. It is very strong. My previous TC was a Palomino and the camper was made that way with only 1/8" skin. Test it out on some scrap plywood and you'll be a believer if you aren't already.
I think your biggest problem will be trying to recover with all the aches and pains after you crawl around for several day under your camper. It was for me.
My best advice: take a Bayer Back & Body before you start every morning and one after you finish.
Just my experience.
Good Luck, we'll be waiting for the pictures.
