Brain, one thought is to hinge the side curtains from the inside of the stationary top sides and let them "swing down" when you need the wind protection. I would agree that when it's cold, you need to keep the wind chill off of you to stay warm.

On my motorcycle you would be amazed at how much more comfortable you are with just "heated" grips during cold and high speed travel. Another motorcycle trick is to put a couple of sections of the morning newspaper under your jacket protecting your chest. It's easy to find "on the road" and easy to dispose of when your done.