You can legally carry your gun across state lines as long as the ammo is stored separately from the gun or guns and if you have the guns concealed out of sight you need a concealed weapons permit.
The only state that doesn't require a weapons permit is Idaho where you can legally open carry or carry a concealed weapon without a permit. But to do so you must be at least 21 years of age and be a resident of Idaho.
If you don't have a weapons permit then the weapons should be carried in the vehicle in plain view and not concealed.
You can only conceal a weapon if you have a concealed weapons permit.