Mounting the CB antenna, antenna selection, SWR tuning follows.

CB is 11m wavelength for all practical purposes.  A 1/4 wavelength antenna
is about 102" long.  About the longest you'd care to mount on your car.
With a significant ground plane formed by the metal roof this solution will
provide the best all-around performance.

Top loaded, center loaded and base loaded antennas mimic the 1/4 wave by
adding components to the antenna to make the RF image very similar to the
1/4 wave.

Modern antenna technology produces the "firestick" and similar short
antennas.

What you would like to optimize is radiation pattern vs size.

Radio Shack sells a tip-up mount that can be used to mount a "modern"
antenna and conveniently hides in the raingutter until you "tip" it into
vertical position..

If you choose a "good" antenna, "match" it as best you can to your
transmitter using a Standing Wave Ratio (SWR) meter you will get the maximum
performance for your CB.

High powered amplifiers (CB is legally limited to only 5W to the final
amplifier which can be functionally enhanced by a speech compression or
power mike)  don't help reception...This still gives you only about 4W to
the antenna..  Making good use of this with an antenna system properly tuned
maximizes both the reception sensitivity and the radiated power.

One of the best is the magnetic mount K-40 antennas.  Low SWR, very good
radiation pattern.

Check with a local amateur radio operator about antennas, they love to "chew
the rag" about radio stuff.

It's always a tradeoff.

cheers,

pensioner (MOS 296.1, 284.2 in a former life)