This idjit got more than he bargained for:
NH Man Pulls Gun On Would-Be Carjacker
The man did very well. Have you thought about how you would draw while seated in your car? There are a lot of pistol courses out there that actually teach how to defend yourself using a gun when in your car. I highly recommend you get this type of training and then take that and practice in your own vehicle (weapon unloaded, of course). This will allow you to figure out what realistically works and doesn't work. If you're serious about carrying a gun, then you'd be a fool not to take this into consideration.