The Maxrad BMT is about as simplistic as it gets. Also check the Larsen NMOTLP which Lexmedic has on his car.
I have a couple of problems with trunk lip mounts. First, the design typically puts a lot of stress on the coax because it has to bend 180 degrees with a short radius. And, as mentioned in Lexmedic's thread, you have to be careful that the setscrews make good contact while not causing a lot of corrosion.