As long as the rubber feet on the rack are nice and clean, I wouldn't worry too much. But if that's not reassuring enough, maybe some of the 3M film will help. In the past I've just put the same towels I use for buffing under the rubber pads. If it's tightly secured it's not going anywhere. Or another way to do it is put down your seat and a thick blanket and use your trunk/backseat until you can get a top mount rack. That's what I'm doing for now. What are you riding? I've got a Cannondale 
