I keep either my PM9 or my SA GI.45 micro in the car in a Oahu holster that's mounted in the door, but the gun never stays in the car without me. I go out, it goes out, I go in, I slip into the door holster so it's ready for me.
Just an aside and a little off-topic ... a recent discussion with a deputy noted that position, and he was so impressed he's now carrying his that way when he's off-duty. He commented that he liked the idea of making a stop and being able to open the door and having access to a perps weapon and being able to get between the perp and the weapon if necessary. Not sure -- no, I know I don't like the sound of that -- but it made him feel better.