To augment my comments above as an answer including photos. I repeat my comments here:
Why would you knock into stuff with a CB antenna? I have an HF, 80-10 meter, screwdriver antenna on my pickup truck. The overall size of the antenna is about the same as an 11-meter CB antenna. The top of that antenna is 11 feet 4 inches from the ground. In the 10 years I have had that antenna on the truck, I have never "knocked" into stuff.
I live in a neighborhood with lots of trees on the streets and arterials and never once have I hit a tree. I never go to fast food drive-throughs. And, if there is ever a time I need to park in a parking garage I stop and remove my antenna and put it in the back seat -- an operation that takes just about 30 seconds as I have a quick release base mount. Antenna is Hi-Q 80/4 with their quick release base, see hiqantennas.com and go to Accessories and see GCD (giant quick disconnect).
The first photo shows the Hi-Q antenna, center loaded, with the top whip antenna topping out at 11 feet 4 inches from ground. You can just barely see the whip part of the antenna on top of the center loading coil.
Second photo shows the quick release base mount and my custom made mounting for shunt coil (which is hidden behind black PVC box).
And, the third photo shows the shunt coil. But, this is not my actual shunt coil I use. This was one of the first experimental coils I built to finally arrive at the perfect match. I adjusted diameter and number of turns on each coil to achieve the matching characteristics needed for 80 and 40 meter bands. Thus coil is nothing but a high-impedance (like open circuit) for higher frequency bands.
Fourth photo shows the VHF/UHF antenna side mounted on the door with a small pass-thru coax cable that passes through the door and the frame cushioned by weatherproof strip. Overall height is about 9 feet from ground.