I have a sheet of Brunzeel Okume plywood 9mm. I can cut a piece to fill the holes. This is the same wood as the interior and back of the house.

Do not use epoxy, use vinylester resin so you can use gel coat on the exterior I think too many people use epoxy when it should be the resin the boat was built with. Having repaired a lot of boats were the owner or repair shop used epoxy and I redid with vinylester. Different story if is a epoxy boat of course.

Just my thoughts. If you are interested ping me?

:: I have removed the instruments out of the express but
:: wanted to fill in the holes left by doing so.
::
:: Has anyone done this? What I was more worried about is
:: what to use as a filler so the interior looks ok. Is a
:: wood plug with fiberglass best? I normally use foam as
:: the filler with epoxy and fiberglass both sides.