Here is the latest version of our truck bed organizer. The bottom level is on the left and holds the shovel, tripod(s), poles, etc. The outer dimensions are 4' wide by 6' long. The front 1.5' is currently dead space, but could be utilized for a water tank or auxiliary battery.
The top level (right) is 5' wide by 6' long. We set it up so that wood is accessed from the left side of the truck, and small stuff is accessed from the right side. Cones and water are accessed from the rear. The center area is "flex" space for random unusual stuff, like a table or EZ-up.
Here is the completed version. You can see that the bottom level is 4' wide in order to fit between the wheel wells, while the upper level is 5' wide so that it (just barely) slides in from the back of the bed. We have it set up so that the heaviest items (pipe and rebar, tools) are at the most forward position on the right side. Cones can be easily accessed by opening the rear window only.