If I was going to buy a truck gun, I wouldn't really want to spend a lot of money in case it gets stollen. For a cheap pistol, I'd go with a sigma if you can get past the trigger. Stoegar cougars are nice for the price. I think you would want something with relatively low muzzle flip if you are shooting out of a car window at a jacker, so why not .45 acp. I think if you are shooting through vehicle barriers, you may be considered excessive in your "self defense" when in court. If your assailant is now under cover, why aren't you driving away from this person, and why are you still shooting at them? With that thought in mind, I think I'd want a .357 like a S&W 686+ loaded with .38's. Less chance of going def from discharging in a car, no brass flying around to distract you, the recoil will be more manageable than .357, and you have seven shots to stop your jacker, or scare them enough to give you time to drive away. That is an expensive gun to leave in your vehicle though. Maybe a cheepy Charter arms .38 would work. Maybe a SP101 as a compromise?