I am in somewhat the same position as you. I have a new Casita
coming next month.
Based on information from the Casita
forum, I have recently bought some BTS All-Surface protectant. I haven't used it myself, but others have with great success. No black water streaks after several weeks of nothing done to the trailer. Big change from before.
It takes several applications on older TT's, but only one or two on new TT's.
You can read up on it at www.cleverinnovations.net
I don't want to be continuously waxing and buffing.