I used a Teraflex mount, with a folding attachment for the antenna. it used all the holes from the taillight, so I only had to drill one in the quater panel for the suport bolt. You dont even really need it, but with a 4ft fiberglass, Its a good idea.
I aint got no ideas for your current mount, although the tailgate hinges seem like a good idea. Ive heard the bumper is a big no-no, bad fuel pump noise.