I took the TN HCP class in June and have had my permit since August.
The responses to the OP were correct in that you cannot have any loaded weapons or magazines, AND the ammo is supposed to be in a different compartment. Ideally either the weapons or the ammo would be in a locked compartment. For those of us with SUVs, wagons, or vans without a trunk or lockable compartment inside, our instructor told us there should have to be more than two steps to get the weapon ready.
For example, if you have your weapons and mags in a bag in the back you would have your ammo in a separate closed compartment or container up front. You would have to open two separate containers to access both weapons and ammo, then load, so that would be three steps. This is not codified in the statute, but she said that it would't be likely that a LEO could make it an issue if you had taken these precautions.
I believe that MS does allow a loaded weapon inside a vehicle without a permit.
Ya' know, it's no big deal to go take the class and get the permit if you really want to stay legal. Taking the risk of being charged and convicted of a weapons crime is not an option for many of us. Also, even with a permit in TN only handguns are allowed to be carried loaded in a vehicle.
Range USA in Bartlett is where my wife and I took our class. Good place, and they give a discount for two classes together, so find a friend who wants to get their permit also. There were people of all different ages and from all walks of life in our class. I was surprised at first, but really, it's not a big deal to get the permit and go packin' legally whenever you feel like it