Personally I use Adam's Polishes Car Shampoo it's the best I have ever used and it's very gentle, but still cleans good.
http://adamspolishes.com/shop/exterior/carwashing/adam-s-new-car-wash-shampoo-16oz.html
Since you can't towel dry it, you should try this blower....I got one a few months back and love it !
You can use it to dry your whole cover spot free...My Dad has one he uses on the grille, mirrors and other stuff to keep them from dripping water for days, but I have found you can almost dry the whole truck with it !
Just search this below on Amazon.
Chemical Guys Professional Surface Air Dryer and Blower