Frequent washing is what has worked for me .
I get up on the roof after every trip .
Palmolive diswash liquid .
9 inch wide brush on a 6 foot handle .
A bucket of HOT water to rinse the brush .
And a garden hose .
I squirt some palmolive onto the roof and wash a section with the soft bristle brush .
Spray off and do another section .
I open the awning and clean it at the same time .
The main thing is the frequent washing .
Nothing gets so baked / caked on that it is impossible to remove .
I use the same method for the vertical surfaces .
I lay down a stripe of palmolive onto the truck brush and wash a section .
I use a washmitt for the tighter spots .
It still looks good after 11 years .
The trick is every time without exception .