That's not cold.
I have kept guns locked in the lock box of my work truck for weeks without a problem in North Dakota. Temperature fluctuations of from -40 (for weeks) to 70 or so just from the heating and cooling. It is more of an issue with your ammo, just shoot the ammo up at the end of the season and keep your gun clean and lightly oiled. I prefer Mobil 1 as it flows well at any temp I have seen.
My rifle and pistol are tools, I am the weapon.