Here's the deal with CB antennas on pickups. If you NEVER transmit (only listen) you can put your CB antenna anywhere you want … under the seat … in the bed ... under the hood or just drag it down the road. During receiving, the antenna is passive. However, where it is located will affect how well it receives. Transmitting and receiving is a reciprocal proposition. If the antenna is installed and tuned for maximum performance in transmitting mode, it will also be tuned for maximum performance in receiving mode. If you NEVER transmit on your CB, you can connect the coax to a garbage can and that will not cause any damage to the CB radio. However, if you transmit into an untuned antenna or garbage can, there is a strong likelihood that you will damage the circuits in the CB radio. And, just because you can hear people talking does not mean that you have not damaged the radio. The transmitting portion of a CB is separate from the receiving side of the radio. You can damage the transmitter and still have a working receiver. In most, if not all cases, if the radio does not have the power to drive the SWR meter needle to the calibrate line on the meter, the transmitter is either damaged or the wire/connections that power the CB's 12-volt circuit lack the ability to carry enough current to energize the transmitter.
Transmitting antennas are electromagnetic field radiating devices. If you install the antenna in a manner that prevents it from releasing its electromagnetic energy into free space, you will not have a functioning antenna. The most common problem occurs when an antenna is installed on the bed of a truck that goes in and out of a garage everyday. In order to eliminate the hassle of screwing the antenna on and off, users will pick a short antenna. That is a guaranteed disaster. The energy leaving the antenna hits the cab of the truck and bounces right back into the antenna. I have owned half a dozen pickups and have NEVER achieved suitable SWR using any antenna shorter than four feet on the front stake-hole. The top one half to two thirds of any high performance antenna MUST be in free space with NO parallel surfaces within its near field of radiation … at least three feet. If radio frequency could be seen like water, you'd see it splattering all over the place. You can't see the RF but your SWR meter will prove it is there.
So … make sure the mount is chassis grounded (with coax detached from the radio). If using a stake-hole pocket mount, especially in the stake holes closest to the cab … use a four-foot or taller antenna. Check and adjust the antenna using an SWR meter. CB's are not plug and play devices. The radio and the antenna must be matched using an SWR meter. There is no other way. Always snug the antenna in place with a wrench because if the wiggle loose, the threads will get damages or break off.
Now … if you don't like putting the antenna on an off … you can do like I do on my "occasionally used" F350. I use a hood channel mount and a two-foot antenna that I tune for the lower 20 CB channels. That is, check CH1 and CH20 SWR and make adjustments based on those SWR readings (see Off-center tuning article here). I never use channels above twenty so I maximize performance on the sub-CH20 channels. This is helpful because the smaller the antenna, the narrower the bandwidth. I also have a pre-tuned 4ft antenna behind the seat so if I ever wanted more bandwidth or increased performance … I just swap the two-footer for the four-footer.
Updated October 31, 2012