I agree with Robb. My first antenna was a K30 mag mount. It works pretty good for what it is. When I tuned it it was amazing how much I had to trim before my SWR was balanced (over an inch). The best you'll see with the K30 antenna is probably going to be about 1.6 on 1 and 40 and 1.2 on 19. I have tuned about 4 of them between 6 cars/trucks and it seems pretty consistant.
The best place for the antenna is going to be on the roof. Especially being a base loaded antenna, that coil should be up above any surounding metal or it will have negative effects on its performance. Many of the mirror mounted antennas you'll see are top loaded fiberglass or the center loaded truckers. Even with the top loaded antennas, for optimal performance 2/3 of the antenna should be above the roof. Also, unless they are co-phased, the system will be directional. For proper co-phasing you should have a minimum of 9' between the antennas. So unless you are driving a rig or dump truck, you won't get proper spacing on a pick-up. You'd be better off with 1 antenna on your center roof.
Now I told you that my first antenna was a K30. I bought a Wilson 1K. I know it is 62" (26" taller than the K30). Bt the stinger is flexible enough that branches shouldn't be a problem unless you are driving fast. I am off road with my truck enough and I don't have much of a problem with it. After 3 years of driving with it and whacking branches, all I've had to do with it is solder the static ball because it was rattling a little. Even when I had my K30, I had to dig it out of the bed of my truck a few times when a low branch took it off the roof.