What screws to use for kayaking?
Let’s start with Kayak Rigging 101- When inside access is available, it is always best to use stainless steel screws and locknuts. Without inside access, you have two obvious choices: rivets or self tapping screws.
The purpose of the scupper hole is to allow water that splashes on to the deck to drain back out and not pool underneath the paddler. Blocking these holes will keep tiny splashes from coming up from underwater through the holes but it will keep any water that makes its way onto the deck from draining back out.
Will fiberglass hold a screw?
Tapping fiberglass actually works extremely well. I have never seen a Sheet Metal Screw Tap, only Machine Screw Taps.
Can you nail into fiberglass?
Put the point of a large nail on the marks and tap it with a hammer forming an indent in the fiberglass. Do this to every mark to assure the drill bit goes in at the exact point you want it to.