not easy to swing a long gun around in a truck.I know you're gonna do what you're gonna do, but in my opinion a handgun is for carrying on your person concealed.
Again just my old fart opinion but a truck gun is for covering different situations altogether.
Just my .02 but if I have as much room as the cab of a truck and a truck to carry it in, I'm going to choose a long gun every single time.
With your budget a Remington 870 or an SKS would be a couple of good options.