What you do not want to do is leave your gun in the car in freezing temps then take it inside where it is warm. The gun will begin to sweat and moisture will build up inside the gun, especially in the firring pin area. Then when you take it back out into freezing temps, the moisture will freeze and could jam up the guns operating system. I go with one posters suggestion of a small cooler. The temps will not vary up and down so quickly. Just like after a day hunting in cold/snow areas. You leave your gun outside to hunt the next day.
US Naval Aviation AMSC 20 years ( retired) ASW/Aircrew Wings, P2V plane capt. Also a Tail hooker, US Naval Academy (DI) Shooting Instructor (Annapolis) NDW shooting team member. VN vet, Bluenose and Shellback.
Alway keep your six covered