Probably the best/most popular way to mount an antenna is via a taillight mount like you can get from TeraFlex antenna mounts
Then mount the antenna using an antenna mount like is shown below, which is a very solid popular way to mount a CB antenna. Just make sure to assemble it properly & place the white nylon insulated shoulder washer properly so it insulates the antenna from the mount.
Mounted via the below antenna mount on a tail light mount, a 2' antenna (like I use) works very well offroad. If you have enough clearance over the top or your Jeep, a 3' would be fine too. But for offroading, even a properly installed & tuned 2' antenna works fine, mine certainly does.
Two good antenna choices would be members of the Firestick FS series family which have a tunable tip for adjusting the SWR. The 2' would be the FS-2, the 3' would be the FS-3.