If you take a look at how full scale aircraft banners are made, I dont think it will be a problem. Basicly you could build a light balsa frame to support the banner. at the end of the banner you make to small pockets that catch the air. These pockets run the entire vertical length of the banner. They are facing forward just like a drag chute. That is what keeps the banner from spinning. There is a book at your public library that shows how to build the full size ones for banner towing businesses. I am sure you can adapt for a smaller one.