From what Nissan claims the bed across is 61.4 inches from the outside edges, I listed two links below that maybe a possibility for tool boxes, hope it helps.
http://www.truckstuffusa.com/deltaaluminumcrossoversinnersidetoolboxes.html
http://www.truckstuffusa.com/steelinsidertoolboxesbydelta.html
http://www.truckstuffusa.com/deltaaluminumcrossoversinnersidetoolboxes.html
http://www.truckstuffusa.com/steelinsidertoolboxesbydelta.html