If you plan on being a basic bitch then the simplest method would be to use one complete sheet as the truck box base but this is both heavy and unnecessary from a structural standpoint.
Homemade sliding truck bed storage.
Next rip four strips of plywood 4 inches wide and cut them to the bed width.
Some beds are tapered so measure each piece.
If you want a sleek look to complement your desire for organization make some drawer slides for the bed of your pickup truck.
Rip two strips of plywood the height of the wheel wells and cut them to the bed length minus 3 inches.
This diy truck bed storage project makes two big drawers and then adds a number of compartments to keep things tidy within each.
We used 6 inch strips of plywood and laid them out across the bed to define the truck box outline.
Start by framing out the base.
Add a locking truck box on top of that.