Larry,

I did a repair like you have many years ago. What I did was drill some
holes around the affected area, to allow it to dry out by letting the
air at it. I also put a small heat lamp above it, close enough to keep
the area warm, but not so close that it could burn. After it had dryed
out I injected some of that spray foam you can buy directly into the
holes to fill the voids. Now you have to be careful about how much you
inject, too much leaves a lump in the floor. I put a weighted board,
larger than the repaired area with holes in the board where the
injection points were (to let out the excess), over the repair site,
and let it harden. Then I repaired the holes I made in the fiberglass,
as well as the hole the water got into originally. When I was done it
looked good, and lasted several years. It might be worth a try.

John