It's been my experience that metal objects that are always left in the passenger compartment of an automobile don't have to be provided with any special anti-corrosion protection other than what would be required to store them inside in the same general geographical area.
That is, if you live in an area where you have to work very hard to keep your guns protected against corrosion due to salt air or high humidity, you'll have to do the same for a gun left in your car. But whatever you do to keep them safe inside will also protect them from corrosion outside.
What will give you trouble is leaving a gun in a car until it's very cold and then bringing it inside where it's warm. Similarly taking a gun out of a cool, air-conditioned area where the gun has become cool into a warm, humid environment will be problematic.
In other words, it's very abrupt temperature transitions that cause the problem, and specifically going from cold to warm in a hurry. The transitions it will undergo while being left constantly in the car will be gradual enough that condensation won't really be an issue, in my experience.
If you take a gun inside where it's warm, after the gun has gotten really cold in the car, you'd better plan to do a detail strip to clean it carefully and get all the condensed moisture out of the works. You might try to warm it and dry it rapidly with a hair dryer as an alternative solution.