Shower dome has been replaced twice

[Rodommoc]

I have a 2000 Adventurer 35U, and the shower dome has been replaced twice, it had been leaking for years. The underlayment is completely rotted away from both sides. The outer dome as well as the inner dome. I replaced the outer dome last year and put new bigger longer screws in, and they bit into nothing. I calked the crap out of it to hold temporarily. I took the inner dome out at the end of the season and left it to dry out. Now I have to replace the wood. I plan to remove the calk and screws from the outer dome, take Luan and cut it to fit then use Kilz to treat it. And slide it into place and screw it back down, then repeat for the inner dome.
All that said to ask this question, what can I use to glue the Luan in place that will not mold? The carpet on the ceiling has to be glued back into place as well; I figure I’d use the same thing for that. I’m thinking something like Liquid Nails.
Where the screws for the domes screw into is just the Luan and Styrofoam. The Styrofoam is pretty much shot, Whatever I use to glue the Luan in place I would like to flow into the styrofoam to fill the screw holes and use it to screw the screws into. (I hope that part makes sense.)
I’m a novice at this part and could use all the advice I could get. I can send pictures as requested.

[Jthigh]

I had to rebuild the frame in the shower skylight in my previous unit. It too was completely rotten. That coach had a rubber roof so I cut relief cuts in roofing material at the corners (diagonally about 3 inches) so I fold back the rubber. This allowed me to remove rotten wood. Built new box (2 x 3,s I think it’s been a while) by putting lag screws into some of the original truss pieces to hold new frame. I built the frame height so I could glue (liquid nails) Luan pieces on top of frame and then countersink some screws as well. Then glued rubber back down. New frame gave me plenty of bite to mount new skylight. I did use put butal tape and self leveling around the skylight seam and screws. I then put 6” wide eternabond tape around the whole thing and the cuts I made in the rubber roof.

One thing for sure, easier said than done. Good luck.

[SuperGewl]

Personally I would go back about 2 to 4" past the rotten wood and cut it out and replace it with new stuff. Also install new foam insulation at least that far back if not more.
What you need is good fresh wood to attach the sky light to in the first place. If you do it right this time you should not have to do it again. Yes it will require some roof work but if you had had done the whole job the first time you would not be doing it again this time.
This is what we call a lesson learned the hard way.