BIG believer that your pistol needs to be in your holster, on your belt or rig. Those guns clipped or loose may end up who knows where in a collision, what's to say one in a door pocket or console that takes a lick is even accessable. A car bump is a common thug tactic.
The BIG reason is that you leave the dang gun in the vehicle, and you get out for something mindless, like pumping gas, and you need it.
I have gone many hours, 6-8 in a veh, behind the wheel, with a full size auto in a belt hoslter even with my pants seam. I am a pretty big guy and had no probs.
I can't begin to count the time with a duty rig.