I installed an NMO2/70 for a friend who didn't want to drill holes in the trunk lid. I used an angle bracket, and attached it to the underside of the trunk lip, just to the right of the license plate. The three screws can not be seen with the plate in place.
Or, you can use the trunk lid, but it does open rather wide, and the whip will hit the top of the car. Incidentally, the difference between the roof and the trunk lid won't be noticeable in day to day driving.