Directly from Dometic A&E manual:
Do not use strong chemicals or abrasives to clean
the awning parts as their protective surfaces can be
damaged. Do not use abrasive or corrosive cleaners,
mildew removers, or hard bristle brushes on the
awning fabric.
• Remove any cleaning solution completely from the
awning fabric. Bleach will degrade the awning fabric
if not completely rinsed off
1. Mix a cleaning solution of 1/4 cup dish soap and 1/4
cup bleach with five gallons of fresh water.
2. Open the awning.
3. Apply the cleaning solution.
4. Close the awning for five minutes, then open the
awning
5. Using clean water, completely remove the cleaning
solution from the top and bottom of the awning
fabric. Rinse thoroughly.
6. Repeat the process as necessary.
7. Verify that the awning fabric is dry before closing the
awning.