I use a couple of simple carrier boards secured to the top of my pickup’s bed to haul panel products while keeping the bed free for tools and other materials. As shown in the drawing, the 2x6s have stop blocks on each end to keep them from shifting from side to side. Ropes that pass over the payload slip through holes and notches in the 2x6s on their way to tiedowns on the side of the truck bed. The carriers can be made to accommodate oversize widths of materials, they are also strong and easy to store.
Dan Jensen, Tigard, OR