The only issue I have with car guns is that a vehicle is a movable object. At any time that vehicle may be stolen, broken into or towed and now you are going to either recover the vehicle, hoping that car gun is there or report it missing, since locally you must do so in 10 days (might be 7, they keep changing it).
Out in the county, while it is still the same, the chance of your vehicle being broken into or stolen is less.
Worst thing to happen is have your firearm stolen and used feloniously.