My engine hatch is fiberglass. It crunched when stepped on. I took it out, and put tape on three sides. I then poured fiberglass resin in and put a whole bunch of weight on top to clamp. Post dry, no more crunch noises.
You might also want to put tape on all finished surfaces.
2002 Newmar Mountain Aire Limited 4370 w/ Spartan K2 and Cummins 500hp
ASE Master Certified (a long.....time ago...)