Suction cups! Horrors! I wouldn't do anything to encourage the paint "off"! And the glass, the sunroof: holy Hannah! the stress placed on the guide rails, the entire system, is problematic (especially in light of the noise complaints and the leaking, etc.). And I would never mount my bike on anything that depends on suction cups. The very idea is scary to the max. I don't like roof mounts categorically. Some of my most frightening "adventures" involved mounting the bike rack to the roof.I have seen suction cup mounted bike carriers. They go on the roof and rear glass.