Hinge bolt breaks or spins

There is a plate bonded to the inside of the fiberglass door jamb 
that has nuts spot welded to it, one for each of the hinge attaching 
bolts (3?);  the spot welds can break, and the nut rotates. The only 
way to fix it was to cut a 2"X2" hole in the fiberglass on the inner 
kick panel, so as to be able to get at the back of the thing.