How can I tighten a loose screw in fiberglass side?

Or use one of those blue plastic inserts...

you can also screw in a helicoil.

Get a larger screw. How thick is the fiberglass?

Machine screws grab fiberglass better than wood or sheetmetal screws.

Drilling the correct size hole for machine threads is paramount.

One can cut a groove across the first 3 or 4 threads to help cut the threads, but a tap is better

Or get a self drilling screw with either sheet metal or machine threads, just be careful driving them electrically



I've tapped fiberglass 1/4x 20 successfully many times through as thin as 1/8th inch fiberglass.

Here is 1/2 inch of fiberglass holding an 800 Lb load.

https://www.youtube.com/watch?v=ZclHNSxr1xs&index=16&list=UUoPqTkOluQsuu3RpGnxVwFw

or wooden matches or dowel rods

I would try filling the hole with epoxy and drilling a new hole for the screw. An easier alternative is to put toothpicks in the hole and see if the screw grabs firmly.

Toothpicks