Hi guys,
"My Radio Shack through glass was installed 6 years ago and the standing wave is still 0 at nearly 4 watts."
There is no such thing as "standing wave 0" because it's a ratio of power going to the antenna to that reflected by it. It can be no less than 1:1 and that's a theoretical, perfect value. The best that can be achieved in the real world is 1.1:1 even on a purely resistive dummy load. It seems what's confusing you is the scale begins with 1, not 0.
As someone said quite nicely a mag mount is the best you can do under the circumstances BUT don't expect the SWR to remain constant unless you leave it undisturbed. It will vary depending on any slight variation in positioning as will it with any transmitting antenna. Hams have found that nothing beats permanent mounting, otherwise all else is a compromise.
Oh Rev, you reminded me of a friend who long ago had a 102" whip and a bumper mount having a weak spring. You can imagine the sway, I laughed myself silly once as he rounded a curve and it smacked a lady square on the butt.