Fixing water damage

[ztyeklar]

I have a 2000 Georgetown motorhome that suffered some water damage in the front on the passenger side. From the inside, I opened up the damaged section and removed all the rotten wood, cleaned off the back of the fiberglass sheeting. I am in the process of rebuilding the damaged area and the part of this process to glue a 1/4" plywood backing to the fiberglass. My question is, what type/kind of glue I should use that sticks very well to both the fiberglass and plywood? Glue that will not degrade with time and will not cause any color change of the fiberglass. Also, it probably should be flexible so it will not crack.
Any suggestion would be greatly appreciated.

[A32Deuce]

I mounted wood in a fiberglass car and used gorilla hair fiberglass bondo. This was in 82 and still driving the car. This was to hold the hinges for an opening windshield. Hope this helps you.