The zip wax is mostly used by people with old trailers that have been allowed to go beyond the point of no return and can not be polished up using more traditional methods.
3M makes some great consumer products for cleaning fibreglass. If you have some oxidization on the trailer their Marine Restore & Wax works fairly well. If you have very little oxidization and simple want to clean off black streaks etc then their Cleaner and Wax
works well also. If you have really heavy oxidization you may need to use one of their designated compounds.
While both products do contain wax & bring out a shine, if your wanting to really shine it up - use one of those products to clean it up but then add on application of a Carnauba wax for a really nice deep shine - but many have started to use the newer polymer wax's such as Mother's FX as they are easier to apply and look pretty good. I used the Mother's FX after using the 3M products and was very happy with the shine - not sure I could tell the difference from the times I used a Carnauba wax.