Firestik cust service guy told me the same Grif...put my mag mount antenna smack in the middle of the roof for best ground plane. OK, tried it, put it through the roof rack, worked OK, looked stupid, wouldn't work with spare tire anyway.
So moved it to rear of roof. "Oh don't worry lady, that strong mag mount will stay put, you'll need 2 hands to remove it!"...HUH! Tipped over before I was even off my dirt road. NEXT!
Got lots of good info from other CB mounting threads and Mark Hardeman had great pics of CB antenna mounted to Yakima LoadWarrior bar. Called Firestik cust serv again, described plan...said it wouldn't work because I was putting some black spongy drawer liner stuff around the Yakima bar...sure as heck didn't want to goober the finish all up!
Said I needed metal to metal contact between Yakima bar and antenna mount I tried it anyway...worked great, so did Mark's.
SWR meter tuned it and it was easily within range. Worked great in Moab.