How old is the trailer?
I know from my boat days that fiberglass and gel coat start to oxidize if left in the sun for a couple of years. That oxidation may be part of your streaking problem. The cleaner wax is getting most of it out but there is still some on the surface.
You could just hit it again with cleaner-wax and have a tough surface that cleans easily.
An alternative for the perfectionist--Get one gallon Of Jasco Prepaint cleaner (sold at Home Depot), mix it 50-50 in a garden sprayer and wash down the trailer, using a soft brush to agitate. Spray it with the Jasco mix again and immediately rinse. This will give you a clean surface with all the oxidation removed. Wax again.
For the guy who wants to wax fast:
Parfe liquid wax. Apply with the same sprayer. No buffing required. I experimented with it on my snowblowers and it is the only coating I've applied on the chutes that keep them clean. I will be spraying it on my trailer in a couple of weeks.
