Apologies for reviving an old thread. I have GMRS as well, and got the FCC license. I mounted the antenna in the center of the Jeep hood to get the best ground plane/antenna efficiency and I went with the most transmit watts that I could find (40W I think).
I still keep a CB in the YJ...a very compact Cobra 75WX that has the tiny but full power transceiver mounted remotely with all controls and display in the mic. Why? Because if I'm on the highway between trails I like to listen to trucker crosstalk and I still run into Jeeps that have not switched over to GMRS and therefore I can still communicate with them on trail.
We had a seriously wounded person on one of our Colorado rides and he went into shock. No cell, no CB...we didn't have GMRS and mountaintop repeaters back then. My rule of thumb is the more comms options that you have...especially if going boondocking, the better.