I know Nissan offers a box that works with the Utilitrack system. I thought about buying it back in 2004. Seemed kinda flimsy and overpriced, though. I'm getting a Delta Fullsize Aluminum Truck Chest Part #896260 (follow link). I think there'll be an inch or so of clearance on both sides and it's about the same depth as the bed. I'll be drilling holes in the bottom of the box and mounting it to the rails on the floor of the bed using spring-nuts. Should look pretty clean. Hope this is along the lines of what you're looking for. I know Better-Built makes one similar to the Delta. I'm sure other manufacturers do as well.