Here is a antenna mount I built for my GX 470 using a framing bracket I found in my local Home Depot isle. It was made from a flat angle bracket. Part# may be in pic stamped into the metal. I made measurements and precision bends. The nice part is it bolts under the existing door bracket in between the door frame near the door handle. Here are some pics, it's made of galvanized steel. I still have to drill the hole for the antenna stud. Then I will finish it with a matte black plastic-dip spray. Stay tuned...
Angle bracket cost $7
Antenna stud $8
Angle bracket cost $7
Antenna stud $8