best method of washing rubber roof?

After cleaning with a brush, and the recommended cleaners( I know, some use a Clorox mixture), once it's dried, you can either spray the protectant on with a sprayer(bug sprayer type) or roll it on with a decent nap roller. I've done both and both cover much better than mopping the protectant on as it leaves streaks.

Spic N span powder and stiff long handled brush. Lots of water to rinse. Chris

TSP, plenty of water and some elbow grease! TSP will not hurt your rubber roof, but will be very good at cleaning it! Get some plastic, to protect the sides of your rig, as you wash the dirt may slide off the roof and stain the sides! When you are satisfied rinse, rinse and then rinse some more. You should get all the soapy stuff off the roof, use a hose if you can! Good Luck!