Wouldn't it bounce up and down quite a bit since the top is not secured? I have been sketching a design that involved couple of custom made bracket and a aluminum crossbar to be mounted between the roll hoops, and the camera would be mounted via a Super clamp with or without a tripod head attched. I've also been thinking about a design where it would automatically turn the camera towards the direction the car is turning. It's a simple design involving a small weight and couple of bungee cords.