What I usually do is hook up a cable lock around the bike, or bikes, and tuck the actual lock inside the trunk. If you pop the trunk, you can fit the lock in between the back of the trunk and the rear window, and then shut the trunk so it cant be pulled out. Then you have at least a cable lock protecting the bike. It's not the best security, but it gives me more comfort to stop at a rest stop or quick place to eat while on road trips.