I think the point is, if they're willing to break into your car (unless you leave it unlocked on a regular basis), there isn't much you can do for leaving valuables in the car where they won't have the will to get there as well. I suppose you could go for bolting a safe in the back part of the cab.
Maybe get a locking toolbox for the bed and stick anything in there? If you get a metal one that would at least be a bit more secure and also not the most obvious place to look for a faceplate.