[DonC]

Chas' post is the tool you want but it's not a perfect fix for what you describe.
The insert leaves a portion of itself above the surface into which it's installed. Very similar to a pop rivet. The insert holds just like a pop rivet does by expanding below the surface of the material into which it's installed. Additionally the hole is going to be relatively large compared to the size screw you'll be using. I'd recommend you locate some of the nut-serts and take a look at them to see if they'll be acceptable.
Another less elegant solution is to use a coarse thread machine screw and tap the fiberglass to accept it. Not terribly strong though.
DonC