The rack on my 90 W150 EC LB was rated at 600lbs. It was the typical full rail angle iron with 1 1/2" tube risers, top rail and carriers. The carriers on my shell I have now are rated at 300lbs. On the 90 I had loaded around 800lbs of conduit without concern, on my current unit over loading is possible but not what I like to do. All-in-all the only concern I had was just the carriers, never the bed. Hope this helps. Mike