Next time around look into using what are called flanged rivet nuts and square base threaded studs. I have been so far unable to find the source for the furniture fittings I mentioned before. Take a look at what is used on a cheap upholstered kitchen chair and you will see what I mean. One type is a stud with a head that is the size of a nickel, but real thin - maybe a sixteenth. The other is a threaded 'tube' that has barbed edges on a nickel sized base - meant to lock into wood. Each of these could be molded right into the fiberglass so that you would have no through bolts, only a fastener on the inside, such as a round head bolt.

Would send pics but not sure how,