Originally Posted by HopCar
I second Whink. It is designed to remove rust stains from fabric. It is also great to remove rust stains from fiberglass
where stainless screws have bled a little. It is hydrofloric acid and you shouldn't get it on window glass as it can etch it.
I was curious, so tried to find the Whink website for more info. Seems to be down for now...
But, if this stuff is indeed Hydrofluoric acid based, be REALLY careful with it. HF is extremely corrosive to flesh (and many other things as well) Deadly stuff if very concentrated.
But, in general, Dacron is resistant to acid attack. Same chemistry as polyester resin... the stuff that most FG boats are made with. If the awning is really Dacron (not often used for awnings due to its susceptibility to UV damage), one of the Oxalic or Phosphoric acid based cleaners might be a bit gentler and will deal with rust stains quite well.
Good luck with your cleaning