My camperback has plastic windows in each of the side curtains. Where the window is sewn into the sunbrella material , there is a small lip of sunbrella on the inside and outside of the window material. When it rains, water runs down the window and pools in this lip until it finally soaks thru the sunbrella and drips into the cockpit.I put waterproofing on a small area of sunbrella and it dried with a sheen and tacky feel.....not acceptable to my first mate. Suggestions ????