HI Andy.
I always have some Milliput in my boat kit, it is good for various jobs, it can be moulded, drilled, we tend to use it for any screws that are loose in the gelcoat such as canopy fixing studs etc. Just take out the screw, mix a small amount of the two part putty and plug the hole, this can be left to dry, drill a pilot hole and refit, or the screw can be put straight in so it can gain its full strength when dry.
Milliput comes in a few colours.
Regards
Alan