3M has several fiberglass finishing products. There are two in particular that look good for restoring the gel-coat finish.
The FIBERGLASS RESTORER & WAX removes heavy oxidation and their FIBERGLASS CLEANER & WAX will remove light
to medium oxidation.
I just bought the RESTORER and tried a small patch on my '99 Casita
and am real happy with the results. I just need to find the time to finish it.
I bought the 3M FIBERGLASS RESTORER & WAX at West Marine.
Here's a link to 3Mô Marine Cleaners and Restorers