How do I install sheets of plywood to make a cargo box in the back of my pickup truck?

well you need to get wood that fits in the pockets of your box usually 2x2's you might have to shave them down a little making sure that they go to the bottom of the pockets. figure that distance plus two feet put all six in (for a long box 4 for a short box) get 3/4inch plywood for the sides for the sides cut it at 2 foot and bolt it on to the 2x2's for the front put a piece in that matches the sides and sets in the bottom of your bed use 90degree brackets screw these in to the side and front 3 places on each side for the rear put a piece of ply wood a little wider than the bed on top and tight on the bottom you can put this one in with the 90's or get tail gate hardware they are called side boards you might have to shave the sides down a little on the back to get the tail piece in hope this helps