I had mine mounted to the spare mount. I did this so it would be out of the way, not getting caught up in trees or bushes and not have to drill into the body. This also allowed the wiring to neatly tuck in with and follow the existing 3rd brake light wiring.
Not the best pics but I can get close ups of the mount and wiring and post later if you'd like.
View attachment 196173
View attachment 196174
That is exactly how I installed my antenna. I removed the 3rd brake light wiring from the hole and installed a PL259. The antenna is protected and no drilling holes in the body.