Ok, got the tile up that was holding the plastic armrest in place and the small carpet piece that holds it to the folding table.
I removed much of the rotten wood from behind, also took off the window trim and removed the wall fabric back to the window curtains.
Also the OSB that is used above the metal and styrofoam structure and below the plywood flooring, it was rotted as far back as the passenger seat and the top of the stairs. Fortunately my tiles were not glued down, just clicked together and caulked to the plastic armrest. The plywood where the rot is were one off pieces that I just removed and will replace.
I need to cut out the OSB that is glued down, there is a seam that I can remove up to just before the seat. Going to use vice grips as the bolts holding the seat just spin, and then remove the nuts from the underside, fun.
Mostly the rot is on the luan, like the pieces behind the ceiling, but there was a couple of hefty pieces that felt like cotton they were so rotten that held the deadbolt mechanism in, centered in the second photo. There was also carpet pad on the floor under the armrest. Wonder if this RV had carpet once upon a time.