Protect All or Liquid Glass or 303

If as you say that you want to bring back the finish then I recommend a cleaner wax for fiberglass, assuming your trailer has fiberglass sides and caps. I like Maguires #50 for that. And as far as 303,it is great for soft materials-vinyl, rubber, etc.but I'd never use it on hard components.

If you're looking for just a wax I personally wouldn't use any of those options preferring something from Meguires like Flagship or NXT Generation Tech 2, which I really like. Several boat waxes are also on my list...Seapower or Collinite. I have used the Protect All but it was not my favorite.