I unroll ours an arms length from the top and attack it going across with Simple Green and a ladder. Then extend it another arms length and do another row across. Repeat until done. While extended I wash the bottom. Yeah it's a PITA but I do enjoy the convenience of just pushing a botton to extend & retract.
Another trick is to spray the Simple Green over the top of the extended awning fabric (and underneath won't hurt), then retract it. Let the Simple Green do it's thing for about five minutes, then re-extend the awning. I have found it makes the scrubbing part go a lot faster.
2016 GM 2500HD 6.0L/4.10
2005 Jayco Eagle 278FBS
Reese HP Dual Cam
Putnam Class V