The advice given in the above post will protect you legally for traveling in ALL States. In a nutshell, the firearm must be unloaded and in a case--preferably locked--in a part of the vehicle not easily accessible to the driver while the car is in motion. Ammunition must be stored separately. To keep it even more legal, I would not store the ammunition in loaded magazines, but by itself, preferably in boxes that are packed in their own separate case.
This is the "Peaceable Journey Law." You're legal to move through a state where the gun is unlawful so long as your destination and departure states are lawful for the possession of the firearm.
The gun must be unloaded and stored in the trunk or otherwise in a locked container -- NOT the glovebox or vehicle console.
BUT -- the other stipulation in this "Peaceable Journey Law" is that you must travel directly through the state. NO STOPS. You can stop for meals, restroom, gas, groceries, but you can't "stay over."
So, no "visits."
This seems like a fundamental infringement of RKBA. Nonetheless, it's the law.
NRA has links and some discussion.
FEDERAL LAW ON TRANSPORTATION OF FIREARMS
A provision of federal law serves as a defense to state or local laws which would prohibit the passage of persons with firearms in interstate travel.
Notwithstanding any state or local law, a person shall be entitled to transport a firearm from any place where he may lawfully possess it to any other place where he may lawfully possess such firearm if the firearm is unloaded and in the trunk. In vehicles without a trunk, the unloaded firearm shall be in a locked container other than the glove compartment or console. Necessary stops, like gasoline and rest, seem permissible.