If you are working with fiberglass parts, you may need to attach other parts, pieces, and features mechanically with fasteners. Bolts and rivets are the most common mechanical fasteners used to accomplish this.
Composites with a nice, decorative gelcoat finish such as boats and RV”s require special care to make holes in them for placing bolts and rivets. Disturbing the area around your hole in a gelcoated surface can lead to very expensive repairs by a fiberglass expert.
You can make holes yourself, but it requires extra care and attention. I found a great Youtube video that demonstrates this from user CenturionCrew.
The biggest mistake that can be made is placement of the hole.
Following the instructions in the video and drilling a nice slow speed hole is the best way to be successful. He also mentions the caution that must be noted to stop the drill chuck from contacting the gelcoated surface. One tip that I have is to place a small piece of rubber hose over the drill bit to contact the gelcoat before the drill chuck.
One other note with holes (all shapes and sizes) in cored composites fiberglass pieces. If there is a layer of balsa or foam core in the cross section, extra precautions should be exercised. One is to coat the inside surface of the hole with gelcoat, resin, or silicone to keep moisture and UV out of the core.
Another concern is compression of the core with mechanical fasteners. Balsa and foam cores typically are low in density, and are not meant to be highly compressed. If you are going to bolt something on, and it is going to be really tight, it is best to use a metal sleeve in the hole that is the same thickness of the fiberglass part. Large washers or backer plates should also be used to distribute the load across a larger surface.