"Breaker 1-9. We got a gator in the hammer lane at the 122 yard stick, that SWIFT driver dun' dropped it." "What the **** was he doin' in the hammer lane?" "Beats me, he'* in a company truck."
One way to do it is to mount the antenna on the trunk. That way there'* not much cable showing, or if you want to drill, there'* not a lot of risk involved.
If you mount it on the trunk, the signal will follow the metal in the car, and will bias the antenna in the direction you're driving. At extreme distances, the side of your antenna with more metal beneath it will reach a bit further. If the antenna is on the trunk you will have better maximum range to the front of the car. If the antenna is on the hood, you will have better maximum range toward the back of the car. This is, however, at extreme distances, maximum range, and is negligible if you're talking to a person just a mile back.
Be sure to tune the antenna to the vehicle, here'* a good write up by fire stick about mounting and tuning the antenna. http://www.firestik.com/Meas-SWR.htm
I had a set of fire sticks before I went to Wilson on my truck. They also make a handy bridge clearance gauge in snow. I had them set 5" higher than my trailer and used them as feelers.