Billy Bob, I've had al lkinds of CB mounts have not really noticed a difference, but all have used high quality 'Maxrad' or 'PCTEL' antennas. Not sure which name is the brand, but we run them for CB, Marine VHF, Cell Phone, Scanners, and the Company radio....it's maybe UHF??? Not sure, I'm not a radio geek. Most of my old work trucks had everythign mounted through the roof, works great, but after you rake the antennas off a few times and the roof gets torn you get water leaks. Now that they made us start driving our own rigs for work, I mounted everything on a cabguard like you are thinking. I honestly have not noticed a drop in CB reception at all with this mount, and I am dodging trucks every day of the week, the worst problem is when they start BSing and don't call numbers.
I've also had no bad luck with stainless whips in bad weather....Olympic Peninsula and SW Washington. One benefit of the cabguard is you don't have to listen to the antennas whine and hit each other and limbs. Here are a couple pics, my old 79 Ford has cab mounts, a cb and vhf marine...ummm...'elk fishing radio'. The Toyota I drive as a work truck has from left to right, CB, VHF, and Company Radio, all work fine and seem the same as a cab mount.
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