I am restoring a vintage fiberglass weirdo-pop up. There are threads in the vintage and the restoration forums. Pic of it is my profile pic. The floor is super solid. I found only one super small area of rot at the rear right corner. The area is about 8x3"...not even a full square foot. It does not seem to affect the structural integrity of the popup, and will not be an area where anyone will walk. (it's in a little storage area under a bench). The lift mechanism does not "push" off the floor like a typical PUP. It's a spring loaded device, so nothing is pushing against the wood. What would you do? Try to cut it out and patch a new piece of wood, or fill it with that epoxy/wood repair stuff...I forget the name.
For an area that small, in a non critical area, I would try some of the stuff xxxapache mentioned or similar, first.. if it doesn't work or the rot gets worse, then I would cut it out and replace it..
I have done a homemade Git Rot approach. I got a syringe from the farm store and injected Minwax Helmsman spar urethane in a piece of plywood that had some water damage.
A wood patch would require some kind of support ... treating the wood or using metal sounds like good ideas to me.
Looking at your photos, and if the wood is not totally decimated, for where the spot is I’d try epoxy first. If that fails then try patching. GITROT is a popular product. Another popular here in the NW is The Rot Doctor CPES. I fairly confident West Marine also has a penetrating epoxy. As mentioned, the key is getting it into the wood. Good luck.
Can Git Rot be used from underneath the camper to seal OSB? I have small corner rot that I can't reach from inside the pup.
You can give it try by going to the farm store and buying a needle and syringe and injecting it into the damaged area first and the painting on a final coat with a thin brush If you do not want to invest in Git Rot, you can buy Minwax Wood Hardener at Lowes/Home Depot and inject it. I recently repaired an area of water damaged plywood subfloor in an out building. I drilled tiny holes and injected the wood hardener. It seemed to do a good job.