Paraguy,
In the vehicle I remove one firearm and have it holstered, or not, in a handy location most of the time. When I do this I have a standard procedure for stops by law enforcement:
1. Lights start to flash, I immediately make sure I am in the right hand lane and signal for a move to the right shoulder or other location when safe;
2. Immediately turn on dome lights;
3. Both hands on the steering wheel at 11:00 and 1:00, and they stay there unless told other wise by the officer;
4. If firearm is not completely concealed (Minnesota does not require disclosure unless asked, and then you must be honest), I state that I have a permit and a firearm in the vehicle;
5. Answer all questions honestly.
I have only once been asked for the firearm, and that was when I was on my way home from league. It was before I had a permit, so my firearms were in a range bag. I had not volunteered the information, but he saw steel poppers from USPSA in the box and asked if I had a gun. I said yes, and he asked for it. He put my range bag on the hood of the pick up and left it there until we were done.
Most responses from law enforcement are professional and verifying permit. While carrying I have never had a firearm taken from me or the vehicle during the process. My last episode had a comical moment when the officer went back to his vehicle he did not tell me to keep my hands in sight, but he did state that he wanted to see the gun in the same location when he returned. The most common request is to see the gun and ask questions about it. I thought I was going to be heading to the range with a State Trooper so he could shoot my LCP one evening. I think we cause one stroke and two heart attacks in passing motorists when he asked to see the guns, and I unholstered my 1911 on the side of an interstate.
As Michael said, know your laws, and the laws where you are traveling. However, this meets the laws of Minnesota, and I have never had an issue.