Here is how I mounted mine when I build my rear bumper/tire carrier. I was going to merely cut and modify my OEM 3rd brake light and raise it up. However, in the preliminary stage of that modification it seemed to not have enough reach and it got a little 'wobbly' being up that high as well as it would have interferred with my Hi-Lift jack mounting bracket that I wanted to incorporate into my tire carrier.
I chose to go a simpler route that would be secure and not have anything hanging above or below to get in the way of anything and still be fully functional regardless of whether I was running the hardtop or softtop.
Here it is without the rear tire mounted.
Here is with the spare tire mounted.