to FiberglassRV, we're glad you're here
I don't see it in your profile and you didn't mention in your post.. what the year is of your Casita
, or if the gelcoat is in "need."
For brand new all molded towables, I'd use Meguires Flagship. If you keep it waxed, it will look good for years.
For an older trailer, with gelcoat that needs help to shine, you may want to use ZEP as mentioned by Norm.
Others will pop in with suggestions too.