http://www.inlandcoatings.com/ I'm happy with this stuff...RC 2000 and look at their "case studies". And also check out Dicor products. Dicor also has a good vid on doing roof.
This rc 2000 stuff I like because it gets into tiny cracks better than Dicor IMO. Hense also takes longer to dry because it is more runny.
Use disposable gloves and brushes and put on 2 coats after first is completely dry. One gallon (smallest size) covered one 5th wheel and one 26 foot class C two coats.
I did my metal roof of my shed year prior to see how it would hold up before doing RV's. 2 light coats much better than 1 heavy coat.
Hate the price though. Around $100.00 a gallon.