You're tempting theft by leaving your cameras and lenses in the car, irrespective of where the car is kept. There is no ill effect occasioned cameras or lenses from hot or cold conditions, but consistently very humid conditions such as those found in the tropics, can lead to the formation of fungus chiefly inside lenses, but on occasion on mirrors, internal viewfinder lens etc. About the only irritation you'll deal with going from warm environment to a cold one is fogging of the lens and viewfinder.