I had this extra instrument hole and I needed to close it up. I thought about how to do it for quite some time. I didn’t want to do the big taper and glass trick like you do for through-hulls but it had to be secure, at least as secure as the instrument that was there. I tapered the hole inside and out so that both sides tapered from large at the opening to small in the middle.
Then I cut a piece of G10 that fit the hole. Luckily my hole saw made a disk that was the perfect size. I tapered this with a sander so it’d fit tight in the hole and did the same with a disk of plywood for the back side.
The inside looks pretty bad but there’s another piece of wood that goes over this and covers up the ugly backing for the fiberglass.
I made some epoxy thickened with cabosil and chopped flock and smeared it on the edges of the disks and on the back of one of them and then put a machine screw in the middle and torqued them down tight. I adjusted the position with a hammer.
When it’s cured I’ll sand it smooth and remove the bolt. Fill the outside with epoxy and microballons, prime and paint to match the already painted cockpit.