I speak from automotive experience, so ymmv...
Dirty streaks are often more of a problem with oxidized paint surfaces. The surface becomes pitted with the oxidation leading to more accumulation of fine dirt and grime. Removing the oxidation will take the stain with it. Wax is the best preventative and will likely reduce or eliminate accumulation of the black streaks that form at run off points.
I would be sure to re-wax any spots after thoroughly cleaning the harsh cleaner off the surface.
I've owned several white autos and they have all been susceptible as they age and the clear coat becomes degraded and oxidized. A thorough wash, dry and good quality cleaner wax followed by a hard dependable wax have always been my solution.
Just use caution on your campers bonded fiberglass, gel coated or otherwise painted surfaces after using harsh cleaners/degreasers. Don't get me wrong. I use them all the time but follow up with good protection for the now stripped surface and am sure to remove any residual cleaner prior.
2011 FR Rockwood Premiere A126 Hard Side
TV=2011 Jeep Wrangler Sahara 2 Dr
Reese 66065 WDH, Curt WDH Shank #17120
Prodigy P2 Brake Controller, Mopar 7-pin Harness
B&M Transmission Cooler (#70268)