I have done some awnings for a major customer that I do sidewalks for. It can be fairly easy to do. I have used gutter zap on them. I use a soap nozzle to apply and to rinse. You need to be careful not to use too much pressure because you can blow the treads apart. Go to
www.doitrightinc.com and find out more about cleaning them. They also have a sealer for them. I will be doing some more after the pollen season and I will post some pictures. I always do the windows with them. It is easy to clean after rinsing with the pressure washer. If you leave the windows dirty it takes away te effect of the clean awnings.