I'd go with the roof rack. You don't want to mess up your interior and door hauling around all that wood. I also think the hitch and small trailor sounds like a good solution as well.

However, It would be awsome if we could open the rear glass on the back door. I'd imagine gas milage suffers greatly driving around with just the driver and passenger windows open. It would be cool if the wind had some where to go to prevent drag.