The most effective and least expensive route,would be flat 1/4" stock,mounted with 4 threaded rods per mounting point. you could also have "U"-bolts custom made,drop them down from the bed rail,and bolt it with the flat stock,to the bottom of the truck frame. The "U" bolts are usually installed in pairs,with a single piece of flat stock,with 4 holes drilled to accommodate the bolts. This reduces the chance of the bed "walking" on the truck frame,plus it gives added security. Depending on the length of your bed,most have three or four mounting points per side. Don't forget your (lock) washers,or "Loctite"! Hope this helps.
