I wouldn't go with a fiberglass. I'd not mount anyplace but on the roof either. Gives optimum performance that way, etc. Make sure if you do a mount other than that, the loading coil(s) should be at least a little above the roof's surface for optimal performance.
I personally ran a Wilson 1k before it got stolen and after that procured a Wilson 5k. I like both antennas. I don't run anything but my radio's 35W pep output.
Just make sure you get the SWR's set right for the frequencies you're going to use and the wilson 1000 or 5000 will do great for anything from a little uniden 510 or cobra 19 to a RCI 2950DX (don't ask how I know it works with one of those, please)...
Mounts for the Wilson 1k or 5k can be solid mounted or magnet mounted. Not sure if you can stake mount them or not, but that'd be sort of not good.
I've been up to about well let's just say slightly into the triple digits on the speedometer but only that fast once with the wilson magnet mount antenna up there and not once did it ever think about coming loose...
