We went to the Eureka Springs Corvette Weekend and I saw some really good ideas for antenna mounts, then came back and fabricated some. They are pretty simple projects.
1. The first is a mag mount plate that attaches to the rear hatch glass. It is a simple rectangle with 2 5/8ths inch holes drilled 2 and 5/8ths inches apart. I used 16 ga steel.
2. The second is a 1 and 3/4 inch wide aluminum strap that is 3/16ths thick and about 16 inches long. I had to bend it in kind of a Z shape so it would drop down under the bumper. This attaches to a flat spot on the frame under the car with 3 bolts. It has a 5/8ths inch hole to attach the antenna mount that is a standard insulated 3/8ths inch x 24 stud. The antenna connection on the bottom takes a standard PL259. I used a 90 degree adapter so it would not stick down so far.
3. The third one has not been mounted yet. I used some 22ga steel and folded the edges to make it stiffer. Then drilled a hole in the end to use an NMO mount. Since I can't bend this one in a zig zag like #2, I will have to use about 1 1/2 inch spaces to drop it below the bumper. I think this will look the cleanest since you will not see any coax. Also my dual band antenna is pretty short so this will be a very low profile set up.
Pictures of these projects are in my Yahoo album here:http://firstname.lastname@example.orgemail@example.com/my_photos
Let me know what you think.