My awning on a 2010 5th wheel STINKS from water that gets between the layers. Once mold/mildew has gotten started, there is no way to stop it other than keeping it dry. Or clean it all the time. I store my trailer at a place that has trailers & motor homes so close, you can't open up the awning. So when we go camping, it's unpleasant and embarrassing. Pretty much, we don't use it, but we would like to.
So I ordered covers via Amazon yesterday, as described below.
RV Awning Covers, Awning Pro-Tech 5 Piece Kit (BLEM), UV Resistant, Snap-on cover for RV Patio awning $89.99 plus $17 shipping.
The same size, for up to 20 ft. wide awning, is about $120 from the manufacturer. Reviews say it's hard to tell what the blemishes are, and harder still to care.
Obviously, I can't say this will work miracles, it won't even arrive until next Tuesday. But the reviews are good, and it looks good to me. So I plan to really clean the awning at the next opportunity, and use the covers thereafter.
If you want to take a look and see what owners are saying, here's a link: awningpro-tech.com