I just use a soft rack so it is not perminate. About a 2 inch thick pad sits on top and the straps go through the windows and connects back on top. The same strap then ties down your cargo with the buckles on the pads. I also put a small towel under each strap above the window to keep from scratching the car. I don't have any pictures but will take some Wednesday if I go out. You could use them to hold down just about anything. Here is a link with some pictures.

BLOCK single surf rack