It's a never ending job. We cleaned roof and entire motorhome including the black streaks (36') w/ slides, and did a wax job 1 month ago. We have traveled about 700 miles and it rained hard the other day -- guess what - black streaks again - Ugh -- We did notice that right at the end of the rain when everything is all wet, the black streaks will rub right off with a damp rag/sponge if you don't let them dry. We will be aiming for almost instant removal after rains from now on. Much easier.
We washed, used streak remover and rinsed. Let dry and waxed.