Bob, depends on what you're trying to do... is it moldy, mossy, greasy, have tree leaf stains, rust runs, etc ? You can wash and wax the trailer using the same stuff you use on your tug (usually). If you have a fiberglass shower stall in your home, you can use that cleaner too on your fiberglass trailer.... stuff like Tilex, 409, Awesome (from the Dollar Store), bleach, 30 Second Outdoor Cleaner, ZUD. Some have even used oven cleaner... working quickly.
If you're worried about what you want to use, ask... or clean a small patch where it's not noticable.
Ten Forward - 2014 Escape 5.0 TA
Double Yolk - 1988 16' Scamp Deluxe