I am thinking about using a u-bold around the roof rack using an antenna mount like this:


Since the roof rack tubes are aluminium and there are rubber and plastic feets holding it I plan to use a no-ground-plane thype of antenna. Since I won't need the ground, I plan to slide a piece of rubber hose on the u-bolt so it doesn't stratch the roof rack too bad. One could also put wing nuts instead of regular nuts to make it easy to add and remove. I haven't decided if I want it removeable or if I will install a fold down mount like this:


Either way, I have to figure out something or I will rip it off driving into the garage