Beachie: i use the RAM with a suction pad mount. No marks left and I am a fusspot cause its my plane. What I find is really neat is that I can quickly rotate the pad out of the way so it lies flat on the dash. This gives full window for landing and takeoff then I block a small portion of the screen once airborn and replace it with the Ipad. I find this setup way better than a knee mount but it depends on the plane I guess, mine is a tandem seater Scout.
Should also work well in a 172.q