Best way to bring shine back to fiberglass body.

Honestly. To bring Gel coat back the way it should be done. You will need to water sand it with no less than 400 grit water paper. Then buff it with a super low grit buffing compound, and then wax it. Yes it is labor intensive. But it is the only way to get the original shine back.

I once did that to a 21 FT boat, hull, and deck. Took a few weeks, 8 hours a day. But when I got finished. It looked like new. And I had new boats sitting beside of it to compare with.