Why not just keep the one on you? A gun left in the car is just something to get stolen, and will not be easily accessed with the same reaction of your regular drawstroke.
I used to keep a model 10 in a thumb break holster strapped to the cage of my work van. Very quick access, and just as secure as if it had been on my hip under the seatbelt. Something to get stolen? Considering I had a minimum of $10,000 worth of tools and equipment in the van at any one time, a $100 model 10 was the least of my concerns.
With the kind of work I was doing, it ruled out just about anything but pocket carry or thunderwear, so my carry gun was not terribly accessible when I was sitting in the vehicle.