Floor rot hey? Darn it! How bad is it?
The ply does go under the wall.
The belly pan is nailed to the edge of the ply also.(if you are trying to pull out some of the floor and are wondering why it's not cooperating).
Here are couple pics.
Attachment 210293
What I did during my floor repairs.
1- Determine patch size.
2- Cut patch with a 45 bevel
3- Lay out the area to be removed.
4- Flip the patch upside down to use as a guide for the multitool to cut out the area. (Having the bevel not only strengthens the repair it also helps with the fitting of the patch...it kinda just drops in place)
5- Cleat the underside of the trailer ply
with 3/4 ply and premium construction adhesive. Fastening with screws. I went for 4-5 inch overlap.
6- Apply more adhesive and screw in the patch.
Hopefully the rot is not to far into the bathroom. I had just a small area.
Don't forget your tanks are under there!
You will probably want to remove at least some of your lower inside skins.
I would also address the rear separation issues. There was NO rearhold down plate on my trailer.
This was ultimately the cause of my rot in the first place.
Best of luck!