For wax, use any good quality automotive wax that has previously given you satisfactory use. I second Norm's endorsement of NuFinish if you're looking for a new product. I have used it on car, truck and trailer for years. It is a premium product at far less than premium prices. The one disadvantage is a slight tendency to show swirl marks although they do disappear after a couple of washes. But everybody has their own flavor; I tried one of the speciality RV waxes, hated it, and gave it to my brother who loves it.
A good coat of wax and using wax to remove black streaks is key to keeping a trailer nice and clean. Black streak remover, Awesome, dish and laundry detergent, (but not auto wash detergent) will all strip the wax off of any vehicle. I will occasionally use black streak remover in a spring clean up, but wax is just as good for all, but the dirtiest streaks and much more environmentally friendly.
I also wax all my vehicles in spring and again in early fall--I am retired you know
. The heat of summer is not a good time to wax anything.