What are your thoughs, concerns and other ideas. Pic attached for reference. Thinking on the center of the top bar above the lightbar.
Some of those LED light bars are known RFI generators. Placing your antenna in close proximity to it might be asking for lots of headaches. Getting the coax back into the truck becomes an issue. Lack of ground plane is going to be an issue.
The third brake light mounts are expensive, they result in a lopsided radiation pattern, they are going to be close to the LED light bar as well as the LED lights in the lamp, and there are lots of reports of them leaking.
Properly installed permanent NMO mounts
-do-not-leak-. That's a story told by hams that don't have the knowledge, skill, understanding, or desire to install an antenna correctly. I've been doing permanent mount NMO's for a few decades now, never had one leak. What you will get is a perfect ground plane, much better performance than the compromise mounts, separation from the noise makers, much more professional look, and no headaches.
I know, people don't want to tackle it, but taking it to an upfitter shop will get you excellent results and you won't be disappointed. While you are at it, having them install a second mount for CB, scanner, GMRS, etc. might be something to consider.
If drilling the hole is really an honest non-starter, I'd probably suggest a fender mount and take the performance hit.