. . . So, as I understand it, technically if I have a good ground I could go with a 1/4 wave and get it to perform decent for trail comms. Anything I am missing?
Nope.
With 2m ham you can get decent performance with a tail light antenna mounting bracket as long as the mounting bracket is well bonded to the body and frame.
Scrape away some paint on the back of the antenna mount bracket and the corresponding area around the bolt holes in the body to ensure a good metal-to-metal connection between bracket and tub. Also be sure that there is a good metal to metal connection between the the antenna mount and the antenna mount bracket.
For my antenna installation I sanded the paint to bare metal around the bolt holes on the inside of the tub as well the outside of the tub and ran a short lengths of 1/2" tinned copper braid from one antenna bracket fastener to an inconspicuous place on an inside surface of the the tub. I added two more grounding straps from tub to frame near each rear corner.
This article on bonding illustrates the theory and the process:
http://www.k0bg.com/bonding.html You can purchase grounding strap on Amazon (called "Tinned Copper Metal Braided Sleeving") and use ordinary crimp-on ring terminals at each end. See:
https://www.amazon.com/gp/product/B01BIBQ940/?tag=wranglerorg-20
I do not use "no ground plane" antennas or any special kind of coax . Neither are necessary in a jeep mobile installation if the antenna mounting bracket and antenna mount are properly bonded to the vehicle. (As mentioned above, NGP antennas are for fiberglass boats, etc. that do not have metal frames or other metal surfaces that can constitute a ground plane. Jeeps installations
do have a ground plane, perhaps not the best of one when one mounts an antenna at a corner rather than the center of the hood, but a ground plane nonetheless.)
As I noted in post # 2 of this thread, a 1/2 wave 2m ham antenna is generally more forgiving of ground plane issues. However, I have used used 1/4 wave, 1/2 wave and 5/8 wave antennas on my current antenna mount without issue. [Photo in post #2.]