I bought a CP-5NMO made by Comet from Universal-Radio. It is pricey although all of the quality mounts I found were. I have had good luck with mine and found it to be very adjustable. I have it mounted on the very rear of my 2001 Prizm trunk lid. As long as your trunk is straight enough to get the actual lip over it, which I would have to think it is, the mount is widely adjustable by each of the hex screws. You can make the bottom main section of the mount come perfectly vertical off from the trunk then use the top hex screw to level the NMO connector. The big thumb screw allows the entire top section and NMO mount to turn probably almost 180 degrees. There are grooves it screws tight into but there are enough of them closely placed that you most likely be able to get it straight up. If you give me until tomorrow night I can probably get a few pics up of mine.
It was hard to spend 60+ on just a mount but I have been very happy with it, as well as ordering it from universal-radio.com