From time to time I have been using my Grand Prix to carry my kayak. Granted, I prefer to use my Honda Odyssey, but I can't have that all of the time. When I do use the Grand Prix, I will put my "Rope Bumpers" on the kayak so it will not scratch up the car.
It's a very simple design with only two parts.
1) Half of a Swimming Noodle
2) Short Piece of Rope
1) Cut the swimming noodle in half.
2) Take a short piece of rope and fish it through the noodle.
3) Place the noodle on the highest part of the kayak and wrap the rope around the kayak and tie it.
4) Do the same for the other half.
Now you should be able to slip them on and off and strap that kayak to your car without scratching it up. Here are a few pictures of what I have done.