This gives you an idea where the plates go and how they reinforce that corner of the pillar I put plates on the forward side of the pillar to strengthen the whole back of the truck. When I started the only thing holding those pillars and the side of the box to the truck was the floor of the bed slash box

The holes you see in the plate will be filled with weld so it gives us a little more weld area hand Shear area to take the stress on the corners of the box