supposedly for good trans/rec you need the twin antennas about 108" apart just like on the big rigs. A center mount needs to have the antenna HIGHER than the rear load to get over for trans/rec. You could possibly go with the long whips but then they are too long when running bare. Lately the sun spots have been limiting trans/rec and last summer we could not talk over a mile between me and another guy traveling with us. We did go to FRS and it helped somewhat, cell phone ended up being the way to talk.
Most truckers dont run the cb like they used to, more into satellite or upper/lower sidebands.