I'm not sure what year your C-class is, but my wife has an '05. I have looked into racks for it, and I think that the roof rack with the fork mount style (with locks) is the way to go. I currently have a Thule like that on my older AMG Benz, but none of it is compatible with my wife's newer car. The trunk rack is a style I have used before and found awkward whenever I needed to access something in the trunk when the bike was mounted, which seemed to be all the time. Just put something in the garage so when you drive up and open it, you have to get out to move whatever it is first. That will remind you that you have a bike on the roof.