capucine is right, the first thing you need to do is locate where the leak is and get that stopped. Take pics and document everything, just in case.
Once delamination starts, it's hard to stop. Replacing the wall is the only fix I know of, but hopefully others may know of something that will work.
I would contact FR even though your out of warranty. You never know, but at least give them the chance to say no. Forest River Ph. Number, 574-389-4600.
You might also think about taking it to your dealer and let them inspect and take pics. FR will have you do this anyway to verify the delam problem.
Gary & Trish
"PT Crew Member Since 11/2010"
2017 Prime Time Crusader 315RST TE 6.0 : 2007 Flagstaff 206ST MAC Series
2012 F-250 Lariat : FX4 : CC : SB : 6.7L Diesel : 3/55 Gears
2016 Nights Camped - 9