gelcoat repair

I removed this old broken humming bird fishfinder. I have a new shinny Garmin to install. But the transom looks like a mess. Any recommendations on how to fill the holes ? Some say just gelcoat, other say epoxy in the holes than gelcoat over top. Oh and there is an old broken screw in there too.

The boat sits in the water all season so I want to do it right.
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