I have a rack above my car. It's a cross-piece with 2 verticals holding it up. It allows side access so I can whip the board straight off the rack and down onto the roof and back again. Side loading is good.
BTW. I am a bit of a neat freak and I hate getting my board dirty and I hate getting salt all over my car. Before I got the bag I was marking the board from the roof racks and dropping salt water on the car.
My method now is to:
Put the board on a piece of grass.
Wipe it dry with a chamois.
Spread the bag out and flip the board onto the bag.
Wipe the other side clean and dry.
Slip it into the bag and pop it on the roof.
I also chamois the paddle and put it into a paddle bag.
Another tip:
I carry a 4 litre water container. You fill it with hot water and wrap it in your towel. It stays warm for 8-10 hours and tepid for 24 hours. You can finish your session then wash yourself down with warm water.