More firepower? What do you guys think is going to happen? A firebase gloria firefight? Gonna set up some foogas?
Carry a handgun for self defense, sure. Use it in self defense? Absolutely. However I fail to see where you think carrying a rifle in a vehicle is going to be of any use in a situation like that.
You going to exit the vehicle? For one if I was outside the driver door and you tried exiting you would be beat silly with the door frame before you could fart. Stay in the car, keep the doors locked, smaller easier to control entry points rather than an open door.
Stay in your car and, god forbid it come to it, defend yourself with your handgun if you absolutely must, however you're not working a rifle inside a car but maybe in one direction left or right, and drive out of the problem. Let the vehicle take the beating, not you.
Taking a rifle into a mob with no back up is only going to give the mob another rifle if and when they decide to stomp you into putty. Being inside a car is much different than being on foot where you can move.