I like this idea, remake the plywood ring then encapsulate in fiberglass/epoxy. I was also thinking about using a big piece of some aluminum flashing and carefully bending/folding it over the plywood ring.
Discussion
If you lay the FG on thick enough, you wouldn't even need the flashing, though, it would protect the gel coat from uv, so it isn't a bad idea.
I meant if not fiberglass then aluminum. Fiberglass alone would definitely last long enough. I just don't prefer working with drippy stuff. I make a huge mess. Much safer for me to work with solid materials lol
Ah.
Do you need the thickness of the plywood? If not, just use 1/8 aluminum got the ring and use a good two part epoxy to affix it to the dome. You can cut a ring with a jig saw. (I'd recommend clamping it to wood as a backer to not bend it much.)