Fred,

while a 5/8 wave antenna has about 3.5 DB of gain over a quarter wave, 
it is also a little over 4 feet tall. That makes it a challenge to 
install a 5/8 wave antenna in an effective place, while clearing the 
garage doorway, or the parking garage roof down town.

So, while it has no gain, don't underestimate the effectiveness of a 
simple quarter wave antenna mounted as high as possible on the 
vehicle. For 2 meters, a quarter wave is only about 19 inches tall. 
Since it doesn't wave around in the breeze as much as the longer 5/8 
wave whip, it also tends to have less signal flutter. There will, of 
course, be some fluttering as you travel. This is caused by the simple 
fact that the antenna is in a constantly changing location in respect 
to the other station.

The method you use to mount it will be driven in part by where you 
wish to install it, and by whether or not you are willing to put a 
hole in a metal surface on the SUV.

One "no holes" option is a mirror mount, which clamps around the arms 
of certain types of side mirrors. Some of these can also be adapted to 
fit luggage rack rails, the top of a rear-mounted ladder, etc. You can 
find them at Radio Shack, or at many truck stops.

If the roof is metal, you can use a magnetic mount, but you don't 
really want that to be a permanent install.
Mag mounts are fine for temporary use on trips or for events, but 
don't leave them there any longer than necessary each time you use 
them.

No matter how strong the magnets, and how tight against the roof they 
hold the base of the antenna, you will sooner or later find yourself 
with a patching and painting problem caused by moisture buildup under 
the base.

I have known of people who clamped a steel plate to a luggage rack 
rail, etc, ran a ground wire from the plate to the frame of the 
vehicle, and sat their mag mount antenna on that plate. The advantage 
here is that you don't scar the vehicle.

If your SUV is fiberglass, or has very little exterior metal, you will 
need to look at a half wave antenna. A half wave is not as dependent 
on a good ground plane beneath it as a quarter wave or 5/8 wave 
antenna. Many of the dual band 2 meter/440 antennas are a half wave on 
2 meters.

Glass mounted antennas are also usually half wave. A glass mount is 
another option, but be advised that some types of automotive glass do 
not work well with these antennas, especially on 2 meters. The 
antennas stick just fine, but the glass doesn't allow the RF to pass 
through very well, and can make tuning a challenge if not impossible.

Hope this helps.

Mike, K5XU