I built custom fitted drawers for the bottom of my pickup truck. This was a long overdue project because I needed to get more organized and I also need to make it my tools more secure.
I bought 4 sheets of plywood for this project. Two sheets of 3/4" and two sheets of 1/2". I also purchased a locking handle like the ones frequently used on utility bed trucks. I cut the top and bottom to fit between my existing side tool boxes. I wanted an extra deep drawer so I cut the sides deep enough to fit my tool box and the milk crates I like to store things in. I also left some space in the back behind the cab for storage crates and infrequently used items.
The drawers were constructed from both 3/4" and 1/2" plywood and glued and stapled together for the most part with screws to hold on the fronts. For drawer guides I used both wood and plastic strips. I recommend the wood runners lubricated with bees wax. It works great.
I finished the box all around with oil based exterior grade polyurethane.