[Richard]

I am not saying you should do this when rebuilding the shower enclosure, but rather giving you something to think about.

When I removed my enclosure for a remodel, I found some signs of water ingress, but not rot. Although I have used Kerdi systems with great success in houses, I felt the flex of a coach required something a little more robust. I stole a page from wooden canoe building. I epoxied a layer of fiberglass cloth on the walls and shower pan making sure to have good overlap at the floor wall seams. It’s not hard or terribly expensive. I used Jamestown Distributors to get the cloth and resin. The trick for smoothing it down is to use a 3 inch mini paint roller handle. No roller, just the steel part of the handle to remove the bubbles and push the cloth flat.

After the water proofing treatment you can go back with whatever wall and pan you choose.