When entering a state you cannot legally carry in, if you unload the
firearm, enclose it either in a box or pistol rug and put it in your trunk, you will be legal.
Some states require that you keep the ammo separate from the firearm. If you have a
vehicle that does not have a trunk, put the unloaded firearm in a “Locked Box” and put it
behind the seat in a pickup or all the way in the back of an SUV. See United States Title
18 - Part I - Chapter 44 § 926A on the Interstate Transportation of Firearms.