RE: shotgun or rifle behind the truck seat.
i keep a 10/22 ruger in my farm truck year round. but i live in an agricultural area. the few times i've been stopped by the sheriff or state troopers they don't mention the rifle next to me. but they do ask if i have a concealed weapon as they see i have a cw permit when they run my plates. were i you, i'd certainly contact my LOCAL and STATE police agencies and ask about local/state laws.