I wash the entire camper (roof included) with Dawn dishwashing detergent and never had an issue.
Big key is to wash it off as soon as possible and not to let it sit on there!
And it is even what the manufacturer recommends:
Wash the exterior monthly with warm
water and a mild detergent.
• Avoid spraying water directly into
refrigerator and furnace vents.
• Immediately remove bird droppings, tree
sap, insects and tar to avoid staining.
• Wax at least once a year with a standard
liquid or paste wax.
• Prolonged storage of unit should be in a
sheltered environment, when possible.
"A mild household soap solution and a soft brush can be used to
clean a rubber roof."
Beau & Sue
2015 Coachmen Catalina 303RLS
2016 Chevy Silverado LT 2500HD Duramax
The more people I meet, the more I like my dogs!