I don't know about the USA, but in Australia, you cannot have things protruding from a window. I was pulled over by a VERY irate cop for having a fishing rod stowed like that. Turns out his normal mode of private transport was a motorcycle. It constitutes a major hazard for them. Now, when i need to transport long goods including timber, i pad it heavily and place it through my moonroof having folded my back seats. This is in a B class Mercedes which is a lot smaller than model S. I have even transported a kitchen bench top i made, this way!! My front seat passenger was condemned to holding it for the duration of the trip to ensure it did not slide around too much, but it worked, did not damage either the car or the wife, and got installed OK at destination some 12 miles away!!
