My concern with appendix carry is that I am more likely to be in a car accident than need my gun, let alone needing it in the car. If my car comes to a sudden stop, that gun is going to be right between myself and the thin seat belt strap trying to stop my body from flying forward. I shudder to think of the damage it could cause.
With a car mounted holster, you have the logistical issue of moving the gun without drawing attention to yourself along with the fact that the more often the gun is moved from holster to holster, the more likely a ND is going to be.
Alas, there are no perfect solutions.
Fly