My son has a 2008 Rockwood that leaked because of a small gouge under the edge of the ac unit that couldn't be seen. He had a quote of over $5,000 to repair any bad wood and new tpo. They also quoted for just removing the front trim and doing an open heart surgery cut back to the ac unit, patch in a piece of wood and glue it and seal it back up $3,200. Without a lengthy explanation of all the stuff he had going on at the time he decided to fix it himself. He figured he could cobble it just as well as they could and did it for $200.
We ended up cutting out less than a sheet of plywood. I dont recall a big problem with the plywood sticking to the foam board. We glued and clamped wood scraps to bridge the joints and let them dry. We then glued everything well and set the patch in and weighted it down.
The ugly part was pulling the tpo back as the felt was stuck real well. We used a razor knife close to the wood in some areas to get it to separate. The only problem we had was with the Dicor glue. The felt that was now on both surfaces didn't adhere well. In the end there were some loose areas so we stapled it down and dicor everything. Half A-- but what are you going to do? He's still using it 2 years later with no problems. He isn't real enthused with Rockwood because the floor had soft spots too.
If I did something like that again I would call Dicor and see if contact cement could be used. I cant see why it wouldn't work with a felt back tpo. Many will tell you that contact cement will damage epdm but it wont. I called Dicor and asked about their glue and why contact cement cant be used. She said the only reason they recommend that type of adhesive is because contact cement is a one shot deal and people would mess it up.
I put an epdm roof on a little homemade TT with a plywood roof. I prepped it well and applied contact cement in sections about 2 feet log. It came out smooth as a baby butt with not one spot or loose area.
The other thing we were able to do is reinforce the cavities around the ac opening. We glued wood blocks in the cavities because the ac gasket compression was collapsing the inner and outer roof panels. Pretty poor construction.
