Rounds can be in the same case, just not in the gun.
I would take the case completely out of the car, remove the gun from the case, load the gun, then put it in your holster.
When returning to the car, remove the case from the car, remove the gun from the holster, remove the rounds, and place the rounds and gun in the case, close the case and place it back in the vehicle.
Basically the same carry as other guns...except it's more of a pain to load and unload.
Myself, I only put a magazine in my Glock, but never actually put a round in the chamber...just quicker and easier.