Originally Posted by Eggie
If the gel coat is not well adhered to the glass resin matrix, it may crack or chip when drilling, use light
pressure and high speed to drill. If a piece of gel coat does chip away, you can fix it back into place if you carefully put a few drops of acetone on the substrate and on the back of the chip, and press it back into place.
Smaller holes should be no problem, but anything over 1/4" could be.
Always use twist drills or holesaws never spade or speed bore bits.
I have found that the spade bits with the cutting points on the outer edges do pretty well for perhaps 1 inch holes.
Those sharp points score the plastic and to some extent stop splintering.
The gel coat is more brittle than the fiberglass base and cracks easily.
Using a countersink to start the location of the hole and drilling deep enough to clear the geicoat from the drill size can help.
Personally I just drill a hole where I want one in my ratty old 1985 Scamp
I have found that fastening a piece of wood from the outside with a stainless screw works quite well, especially when the ensolite or other covering is cut away and glue is used as well.
That is how everything in my trailer is held in place.