Please note:
Does not fit with previous generation DECKED drawer systems

A weatherproof drawer system is of course also suitable for use on pickups without a hardtop or tonneau cover.
Not all vehicles have lockable tailgates, though! And even if they do lock, you don't necessarily want the drawers to be accessible when you use the central locking system...
Hunters, for example, might appreciate individually lockable drawers! But the locks also make sense on construction sites, parking lots, and campsites.