For some reason your pictures have been removed. You know what you have to do, though. I'd suggest, when you have everything removed and new, good wood installed, spray the area with an anti-fungal solution. I just use diluted bleach and an old Windex bottle. It will stop some of the wood eating microbes and eliminate any mold issues, real, or imaginary. I say that last because folks are now moldaphobic, IMO.
FWIW, when I tackled the bad floor spots in my rig, I got lucky. I was able to replace bad plywood under the walls by pulling all the fasteners and sliding the new sheet under the wall.
As MFL suggests, using foam board to replace the fiberglass batts is a real good idea. I was just checking on a new-to-me foam insulation board I'm using, Insulfoam. At 70f, the moisture penetration rate is <1%. The absorption rate is <3%. R rating is R 4.5/in.
In the restoration thread in my signature line, "The Cowboy/Hilton", there are pictures of the extruded foam I installed, throughout.