I tackled that job on my last RV(a Class C MH).
After peeling off the rubber membrane, I found some rot in a couple corners of the plywood. I cut out the 3/8" plywood around the bad areas and found rot in the 2x2 ceiling framing and water soaked beadboard (white foam insulation board). The beadboard was like a sponge. So I pulled up
ALL the plywood and removed the "sponge" board. Without damaging the interior ceiling board, I cut out and replaced any rotten 2x2s. The 2x2 framing around the AC vent opening was weak and inadequate so I doubled up all the 2x2 ceiling joists and AC/vent openings with liquid nails and screws. Since everything was open from the topside, I added wiring for those extra little things like a MaxxFan, outlets, and speaker wire. Next I installed blue XPS foam board and glued and screwed 1/2" plywood to cover everything. There was no flex at all when walking on it when I was done. Next I filled the screw heads with plastic wood filler, installed the rubber EPDM roofing with the roof glue, cut out the openings and installed new molding trim using putty tape and stainless screws. Last, I installed new vents, a new AC, new tv antenna and drizzled the Dicor over all the topside screws and such. Took a few weeks for the entire project working inside my polebarn.
I wouldn't care to do it again but it really helped in the resale of it.
Me'62, DW'67, DS'04, DD'07
'03 Chevy Suburban 2500LT 4WD Vortec8.1L 4L85-E 3.73 CurtClassV
'09 BulletPremier295BHS 33'4" 7200#Loaded 1100#Tongue Equal-i-zerHitch Tires:Kumho857
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