I've used Nu Finish on our Escape since it was brand new. It has always been top or nearly top rated by Consumer Reports at a reasonable price. Our Escape is stored inside when we aren't traveling, so the Nu Finish lasts for a year before we need to reapply. I find that if I keep the trailer polished that that the black streaks wash off easily with regular car wash soaps. The other Nu Finish product, Scratch Dr, takes off any more stubborn streaks and works well on bugs and road tar. It does take a bit of elbow grease, but it doesn't remove the wax, in fact it leaves a good shine after use.
Eric (and Mary who is in no way responsible for anything stupid I post)
"Beware of false knowledge; it is more dangerous than ignorance." George Bernard Shaw