Please don't store a firearm in a car. Cars are not secure, and any hype breaking glass for your stereo becomes an armed hype.
The best place to carry a pistol while driving, is on your person. If you crash and / or have to get out in a hurry, chances are you're going to have to go back for your gun.
This may not be the fastest way to retrieve it in a hurry, but its safe and thief-proof.