Streaks coming down from the roof are caused by dirt and debris that settles on the roof as it sits, just like the stuff that settles on the roof of your car if it sits outside. There are many coatings that you can put on your roof, but NONE of them will prevent dirt for accumulating on your roof and causing streaks when it rains.
The front cap on my coach is fiberglass and it is painted and the heavy gauge aluminum roof is also painted. I keep them both waxed, but I still will get streaks from the accumulated debris and rain.
They do make an RV gutter that can be used to prevent water from draining down the sides or front of your coach and installing the gutter is not that difficult.