I'll chime in with a "rule of thumb" here.
If you don't know the local laws of your state or your destination state, the rule of thumb is to store the gun unloaded in a locked case, where the lock is a key-lock built into the case, a key-padlock or combination lock. Ammo should be stored separately from the firearm. Do not store your firearm in the glovebox (or with your car's registration papers).
Research is key here. Utah has pretty reasonable requirements. Colorado can be spotty (especially in urban areas) with more restrictions.
Also beware of the actual, legal wording of the laws. In California, for example, it is illegal to have your pistol magazines loaded, even if they are separated from the gun. (Interestingly enough, loaded speedloaders are okay). Other states may have similarly oddities regarding transporting of firearms.
