Not sure what a "long period" means, but...I'm pretty lucky in that my truck is line of sight to my office, so it's less of an issue as if it were out of sight in a Pkg lot or Pkg gargage or on the street.
I leave my Kimber in the consol, vehicle locked, unloaded, out of site....when I am in the vehicle, I comfortably carry it on my belt, loaded or may have it in one of the cubby's....if I have to be somewhere that I don't think leaving it in the vehicle is a good idea and I can't OC then, under the shirt it goes! I don't get to far from it, having had vehicles broken into in the past.
...mostly, when I'm in the vehicle, I just wear it....
I started carrying with one in the chamber and when I get to work I have to leave the gun in the car. When I remove my gun from the holster I remove the chambered round to store it but wonder if that’s a good idea or not. How do other people handle storing a gun in the car for long periods?