First off I keep the roof clean and make sure there is no algae or debris build up in the gutters (leading cause of black streaks). I try to wash roof two or three times yr.
I wash the sides as needed to keep clean and new looking with nothing more than Dawn/water and a soft bristle brush on extension handle.
I hand apply Nu-finish polish once annually on all fiberglass and windows and on the front cap 2 to 3 x year. Really helps repel dirt and black streak stains.
I have been using this process for many years and keep my rigs and decals looking good. I am rather anal about keeping it nice so I guess it never has much of a chance to get dirty.
Steve
Steve Rinker
Rochester, NY
2013 Keystone Sydney 340FBH 5th Wheel, 12,280 lbs loaded (scale)
2015.5 GMC Sierra Denali 3500, SRW, Duramax, CC, Payload 3,700 (sticker- not scaled yet)
Take my posts for what they are, opinions based on my own experiences.