My thanks to all who have responded. Lots of good ideas coming in. Keep them coming.
I don't carry as often as I should and more than once I have been at a stoplight with some idiots' radio blasting stupid music or their bass vibrating MY truck. No incidents yet, but there is always the 1st time. And with the current state of affairs, it is always better to have and not need than to need and not have. Thus the reason for the post.
I am a wheelgun fan (old school that way), but my EDC is a S&W Shield .45 so I am leaning towards getting another one for the truck and keeping 3 mags with it. If 21 rds won't get the job done, I am already in a world of S&%T.
Just to state the obvious, but of all the reasons to have a dedicated vehicle gun, stupid music or loud bass would not even be on the list. If you're getting into altercations over it then you're doing life wrong. (Not saying you are, but seems odd that's the primary thing you listed.)
Anyway, the best approach for me has been to carry a gun everywhere it's legal. I'm going to go to my EDC if I need to fight from the car. The idea of a dedicated vehicle gun has always seemed a little odd to me when I've already got one on me. But to each their own.