Doug, one other thing that I should have mentioned earlier: lots of people swear you MUST have a 19/32nds-wave (or whatever) loaded whip to communicate from your car. I've had 5/8th waves for 2m and never noticed any really significant difference between them and quarter-waves, in overall performance. There are just a bunch of other variables affecting how solid your mobile signal is. But the big advantage (IMO) to a quarter-wave like the Buxcomm one I sent the link to, is that it's short enough to go on your car's roofline and still fit into most garages and other low clearances. Being up above the rest of the car adds a lot of performance, even if it IS shorter than a 5/8ths.
One other BTW: if you like homebrewing antennas, and it IS a world of fun, when I first put a 440 antenna on my car, I just made a dualbander with 2m and 440: I used a piece of brass rod to make two quarterwave verticals, one for 2m (19") and one a bit over 6", joined at the bottom in a simple 3/8" loop. A 3/8x24 bolt about 1/2" held the two vertical antenna elements in the mount, basically giving me two quarterwaves, close together. It was ugly as can be, but both bands worked great, and it cost me less than a buck and a few minutes of my time.
I just ordered the Buxcomm one (I think it was $8 when I ordered them) because it looked nicer and it was too inexpensive to turn down.
Again, GL, 73, and this forum is always glad to provide advice! (Sometimes too MUCH advice, but that's another story!)