You can simply impregnate the awning or boat cover with Sprayhood & Tent Protector. If necessary, remove the window film immediately after impregnation with a damp cloth.
If this impregnating agent dries, it can leave small stains on the windows. They are easy to remove with the special window cleaner from Ultramar.
In our special sail & tent laundry, we use this impregnating agent to impregnate and waterproof all awnings, boat covers and catering parasols. We do that by immersing. We find that it gets on the window film as well and that is never a problem.