What causes the black streaks on the side of my camper?

Black Streaks are the result of contaminants, such as dust, road grime, pollen, minerals pollutants in the air, and moisture that collect on a horizontal flat surface like the roof.

The mixture slides down and sets on the vehicle surface when the moisture evaporates. The process repeats daily and with time streaks appear. In addition, black streaks set on surfaces that are not cleaned and waxed regularly.