I agree, 303 Aerospace Protectant is a great product for boat use. I use it on all vinyl and rubber that is exposed to the sun. It has a very high UV sunscreen and does not leave an oily film. I first clean the vinyl then add a light coat of the 303 every few weeks. If you store the boat out of the sun, you don't have to apply it as often.
As far as wax, I found that natural waxes don't last that long and have to be reapplied every few weeks. What I do is prepare the fiberglass with a good polishing compound. This gets rid of all the small scratches and helps to reduce the pores in the fiberglass. I then follow up with a good poly sealant. I have found that the Poly sealants last about 6 months.
The products I use are, Zaino All-in-one, but you could use 3M Perfect-it 3000 Swirl Mark Remover if the surface doesn't have much oxidation. If it has a lot of oxidation, then I start with 3M Perfect-It 3000 Extra Cut Rubbing Compound, followed by the Zaino AIO or the 3M Swirl Mark Remover. Once the fiberglass is shiny and smooth, I use a polymer sealant. The product I like best is Zaino Z-3™ Show Car Polish, but you could use something like Meguiar’s #20 Polymer Sealant. What I like about the Zaino is that you can apply multiple layers for added protection. I usually put on two or three coats. Most other products, especially cleaner waxes, remove the the previous layer every time you add a layer, so the most you can have is one thin layer of protection.
If you stay on top of keeping the boat clean and polished, you don't have to use the polishing compound again and only have to apply the sealant every 6 months or so. Since I keep my boat covered and in a garage when not in use, I only have to apply the sealant once a year.