Did a quick search. I've seen a few different configurations on various shows and articles online.
http://www.tactical-life.com/online/products/universal-vehicle-handgun-holster-mount/?right=related
I made a kydex holster for a friend of mine and he wedged it inbetween his seats. Sits next to him as if it were on his belt.
I have it next to me. I'm just showing the OP there are many options.
I need something for a Beretta PX4..
This is how I roll!