Personally, I'd steer clear of the fiberglass antennas. They are too stiff, and contact with a branch at speed will likely damage it, even with a spring.
I'd strongly recommend a Larsen NMO27 with a spring.
Stainless steel whip, about 49 Inches long. You can add a spring (you'll have to shorten the whip).
I used these for many years on top of full size trucks and SUV's. They'll stand up to the beating, even without the spring.
It's not a consumer grade antenna, so don't expect consumer prices, but they really are not that expensive. They'll perform very well if they have a proper ground plane underneath them.
If done right, it'll be the last CB antenna you'll need to purchase.
Take a sniff around here:
http://www.theantennafarm.com/catal...-low-band-194/25-31-mhz-cb-10m-high-gain-447/
You'll need an NMO mount for it.