You can make good side curtains in a few hours out of Magard - Lexan and specific rubber moldings. I've done it a dozen times with 98% rain proof . Roll up windows will not work, the windshield needs to be pulled rearward at the time the car is assembled ( CMC did this on their roll up window cars & IM does this on their speedster.... AL Shapiro has one .) This allows for alignment of the forward side glass to the windshield frame, you would also need a specific windshield frame to side glass rubber. I have looked at doing this a few time and said pffffst! to that .