I did a very basic version of what you have, I did full length pull out drawers. ply wood top and bottom with a 2X6 side and a divider. The drawers are 1X6 sides with a ply wood bottom. The top is just wide enough to slide in through the tail gate opening. I used role on bed liner from Lowes to paint it. If I could post a picture I would, but for some reason I can't seem to post pics.
I wanted to do something like yours, but I am just not that good with a saw and a tape measure.