Carried empty you will be OK but it will be useless locked up when and if you need it.
I won't argue with that. But I think some are blurring the line between a "truck gun" and a defensive weapon.
The truck gun is a rifle, carbine or shotgun, "carried onboard", so it is available when the opportunity arises to legally take game or control predators/ pests. Its not there to repel boarders at a moment's notice, though it will work for that if the situation allows.
It is carried in them vehicle unloaded (chamber empty ALWAYS!!!) for SAFETY reasons. If the law requires the entire gun to be empty of ammo, in order for it to be legally "unloaded", then that's the way you do it.
(semi autos with detachable magazines make this simple and easy).
The truck gun (or trunk gun) in your truck, car, boat, plane, is there so it can be there. So you don't have to go home to get it, then come back to where you want to use it. You stop, get out, get the gun, load it, and then go after what it is you are hunting.
Hunter safety has, for GENERATIONS taught how stupidly unsafe and dangerous it is to have a loaded rifle or shotgun in your vehicle. They used to show kids actual photos of people killed because of an accident with a loaded gun in a car, etc. REAL DEAD PEOPLE, real blood, real gruesome reality. Pictures that (in the 70s) were too graphic to show on TV or print in the news.
I don't know if they still do this or not, but they used to. Chamber empty makes it safe, physically. Laws go further, on purpose.
The loaded pistol in a console or glove box etc., is a different matter. It's NOT a "truck gun", even though it may be in your truck. It is a "nightstand gun", that just happens to be in your truck. Loaded and ready, not on your person, in a reasonably accessible storage location. Just like your bedside night stand drawer.
Today, this is only legal in some places, with the proper permits, and in some places its not legal at all, and to have a loaded gun in your vehicle it has to be on your person.
The truck gun is the rifle, carbine or shotgun, or handgun carried onboard to be available for sporting use. Not as a primary defensive weapon.
A handgun (or other gun) carried for defensive use should be called something else.