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.
Custom built shelving with sliding drawers serves as the base with a sturdy top to cover the entire shelving area so you retain the use of your truck bed.
Next rip four strips of plywood 4 inches wide and cut them to the bed width.
We used 6 inch strips of plywood and laid them out across the bed to define the truck box outline.
The drawers look great while hiding your precious cargo.
Add a locking truck box on top of that.
Based on the concept of furniture sliders this is how i built my chevrolet avalanche truck bed slide.
This diy truck bed storage project makes two big drawers and then adds a number of compartments to keep things tidy within each.
Start by framing out the base.