BradZ - Judging from your member badges, I am assuming you already know a CWP is best. My guess is your thought is how to keep a weapon in the truck for defense but also keep it from getting stolen or played with by a young child's hands when you are not in the vehicle. Besides, even with a CWP, you can't take a weapon with you wherever you want to go.
Now, that being said, I recommend a CWP anyway but I personally would not lock a weapon up in a safe either. You need to be able to access it quickly and effectively. Your call on that one. Flash mobs are rare and typically only occur in large metro areas. But, preparation is everything. Just figure out what works for you.
A WOT could do much more damage than a firearm anyway. If you find your truck surrounded by an angry mob, step on the giggle stick and get out as fast as you can. Running over one or two of them will make the others move out the way quickly when they see you mean business. If that does not work, then having one of these babies for close range work might help...