I too have that alum coating. They call it Krystal coat.
I use regular car wash detergent on it with a long car brush. This works well on the bugs and road grime.
For the black streaks there are a variety of cleaners out there. I have tired many but the one that works with much success is called Awesome. You find it in the dollar stores.
On the black streak areas the car wash will not get off I hose with water, spray on Awesome, car brush scrub and then rinse. Black streak = gone. It's amazing.
Note: This will strip off wax and most likely any UV protectant you have on the fiberglass panels. But it works on the black streaks. So if it getís on the panels, you have to re-apply the UV coatings.
Simple Green works some too but not as effective as the Awesome on real sun bakes streaks.
You do not wax the Krystal coat siding. Once clean it shines
To help prevent black streaks is to keep a clean roof. That dirt and grime up there leaks down and causes the streaks in the first place. So I wash the roof about every 3 months when it is outside. I use warm water and Tide, and a car scrub brush and rinse before and after. This is out of the Sunline manual.
It is a job doing the roof and siding all in one cleaning. Every time I do it, Iím sort of glad I only have a 26 footerÖ. But it is nice and clean after words.
The other words of help are, stay ahead of the cleanings. Meaning when build up occurs get to it before it is sun baked on to death. In my case I wash the outside about every 4 to 5 weeks and I camp about every other weekend almost all year.
The best way to keep clean is what I found this winter. I finally fixed my out building so I can get Sunny inside. This option is not available to everyone I know.
Hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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