I retired from house remodeling, so dryrot is what I did .
I would not bet on not falling through.
On my Fleetwood aluminum frame was only on side walls, where main bed floor was having 2 pcs of 1.5 x 1.5 wood.
Such frame would not support human weight on its owns, but sandwiched between plywood with glued Styrofoam it does.
In my case, the outside fiberglass had a joint right under the nose, so I was able to pull it from there and exposure the frame. I put solid 2x6 there and screw it to aluminum frame on the side.
Than added smaller frame between.
Hardest part was gluing the skin back. I was using construction glue, who takes couple days to dry. So having 2x6 as pressing board, I was gluing about a foot of skin at the time, so took 2 weeks to process.
Good luck on the repair.
