Looks like iron or tar deposits. Look up www.CarPro-USA.com
there is a product called Iron-x and Tar-x. Spray it on and it will dissolve the iron deposits and rinse off. Also look it up on YouTube and check out the videos. I use it works excellent.
I have iron in our water that leaves iron deposits in our shower and it takes it right off. Professional auto car detailers use it also.
If you go to [url=http://www.CarPro-USA.com don't be surprised if you buy some other items also for your RV/Car finish. They have some of the best car products on the planet. No you won't find the stuff at any Wal-MART or Auto Parts place.. They have ceramic coating for your paint that's rated in years as to how long it lasts.
2014 Palomino Columbus 3650TH
435AH 12V VMax Charge Tanks, 520 watt Monocrystilline Solar Array, Morningstar MPPT TS-60 CC,Morningstar Remote,Cotek True Sine Wave Inverter,Cotek Remote Controller,50amp Progressive Hardwire Surge Protector
2015 Dodge 3500 6.7L 4X4
2011 CanAm Commander XT 1000