Provided the fibreglass is thick enough, another way could be to use "nut inserts" ( that's what they are called in the UK, I don't know if they are called something different in the US; they are basically an insert with a tapered coarse thread on the outside and a machine thread on the inside. There's a very thin flange on the outer face, meaning they can be screwed in virtually flush, using an allen key. They are usually used in wood, but I have succesfully used them in fibreglass; the drilled hole needs to be the correct size though, to prevent cracking. I haven't found it necessary, but a dab of something like epoxy or 4200/ 5200 PU would ensure they can't unscrew. The old holes from the original screws can be used as pilot holes, in exactly the right position.
If the fibreglass isn't thick enough to take these insert, it's not really thick enough to put screws in either and nuts,bolts and washers would be best!
Graham
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