Du-Ha makes these. A little pricey for plastic
Don't think they have any enclosed/lockable options tho.
A friend made his own out of wood. And made it a bit deeper. Made a hinged top with a cylinder lock mechanism. He wrapped it with matching interior carpet and it looks great. No pics tho sorry. Just an idea.
I have also seen the wheel well tool boxes mounted sideways to the rear of the cab. So you open the 1/2 door and can access the box from outside the truck.