If you get stopped and have a gun in your truck and you are carrying it the way you have to in that state and yes there is as many rules as they are states this is what will happen, They will take your gun unload it put in their trunk when you are finished they will hand it back and say do not load it until you are down the road. I know been there done that.
And in North Caroline you have to tell if you are carrying very soon after they start talking to you. My permit is good in 33 states and one of them is not IL. so if I am passing through that state the gun is unloaded and locked up if I stop in IL. to unload the truck then I am braking the law