Those type of tool boxes are low security, too easy to break in to. If you are serious about your tools get a Knaak or a Greenlee strongbox. Bolt it to the floor or to the back of the bed. The hinge is the weakest link, but if you bolt it up tight to the bed they can't get to the hinge too easy.
Of course, depending on where you live, they might just take the whole truck.
