A trunk mount will pretty much always give you a compromise location at best, as well as a compromise connection to the metal it is connected to as well. In my experience magnet mount antennas tend to have better connections that lip mount antennas. I also point out that the trunk lid (or hood for that matter) of the car are rarely the best locations as their connections to the rest of the car tends to be iffy at best. If you run power (a lot less than many people think actually) even rf bonding it is rarely enough.
I am not saying an antenna in such a location with such a connection won't work ok, but you are adding adding together several compromises so it definitely won't work as well as an antenna bolted to an optimal location on a car (the middle of the roof).
Also don't think that just because it is a trunk mount it will cause less damage than drilling holes, you are connecting to a thin piece of metal remember, winds over time (aka highway driving) can still bend the metal, possibly costing more in damage than plugging a few holes and repainting. Yes I have seen it happen before. Although you can get around this by using a smaller antenna on the lip mount, but then you add yet another compromise to your already compromised antenna.
The DB