mmckenna
I ♥ Ø
You will need a ground (plane) independent antenna due to the mounting location. AKA 1/2 wave.
Comtelco A1812-44 VHF 1/2 wave no ground plane bright finish is what I use in applications like yours.
Mmckenna has the part number from his favorite manufacturer.
I used the Comtelco A 1812-44 on another Jeep with a bracket similar to the Teraflex, and it works well, SWR is well within limits. I did use the 3/8" NMO mount, just reamed out the hole. Jeep has fiberglass top.
I'll second this.
While I like my Larsen antennas, I do have a few ComTelco 1/2 waves in use. Two of them are on Polaris Ranger UTV roll cages. I went with the spring base models. Both of them have taken some high speed branch strikes without issue. One of them even has a permanent kink in the whip a few inches down from the top.
You can't go wrong with a name brand antenna from one of the big commercial manufacturers. Larsen, Comtelco, Antenex, Laird, etc.
Do stay away from no-name brands off e-bay as well as the Tram and Browning lines. Tram and Browning (both the same company) are made in China. The build quality isn't the same and they've only been on the market a few years. You might save a few bucks, but you'll end up purchasing a better quality antenna down the road. The few bucks you'll save won't help you when your antenna fails and you're 20 miles down a muddy trail in your Jeep. There's a reason why the public safety agencies stick with the name brand stuff.