I've decided to remove the stereo and speakers from my bass boat. Lots of reasons....outdated, poor quality, speaker covered by flipping deck, etc.
I plan to use a portable radio/bluetooth speaker that I really like.
My question is this..... the radio and speakers are currently installed through fiberglass at the left of passenger seat and in the driver console on left side and front. What method and materials should I use to cover the holes left behind?
Any ideas out there?
Hit me.

Starboard would be the cheapest. Wouldn’t need to be thick.

I would just rivet .040 alum over the holes and seal it with some silicone. You can paint it to match.

Marine lumber is an option since it is tough, easy to cut and shape, and is UV protected.

Bondo over mesh

Personally I'd just leave them in place and not use them anymore. Unless your having the fiberglass professionally patched up.

Black starboard to cover the speaker holes, and the same for the radio but since you have power there, I would add a LED interior light.

Aluminum plates or Lexan over the holes and I would paint them flat black. I made some for my boat out of aluminum then covered it with a layer of graphite then shot clear coat over it. I removed a flasher in the console and covered the hole. I glued it on with clear silicone and that worked great.