Trunk lip mounts can be a mixed blessing. The trouble with them is that you have to tighten the screws down pretty hard to bite through the paint. Getting through the paint gives the connection to the ground plane. They usually require occasional re-tightening and rust/corrosion issues are a possibility. They'll work, but I don't personally think they are much better than a magnetic mount. This mount: http://www.theantennafarm.com/catalog/larsen-nmotmb-1873.html
would probably be a bit better as you can make a good physical connection into the vehicle body. That physical connection makes for a good ground connection, which helps performance. Mounting these off to the side, where they usually go, isn't as ideal as mounting on center, but it'll work. Putting this mount back by the trunk, or even up by the hood works. Just keep in mind that you have to route the coaxial cable up to the radio. That can be a task on it's own, so keep that in mind when choosing a location.
NMO-27c is a good antenna, like I said in an earlier post, I used and installed many of those back in my earlier days. I set up a lot of friends with permanent mount CB antennas on their trucks. I always used those antennas and never had an issue. Hard to beat an NMO mount for ultimate flexibility.