Originally Posted by
Access Roll-Up Cover
There's more than one company that makes a soft roll-up tonneau to work with a toolbox. As others mentioned in this thread, the Access Roll-Up Cover is a great option and it's designed to fit behind most 20" - 21" over-the-rail toolboxes. You can get more details on installation and applications here:
Access® Toolbox Edition Truck Bed Covers and Caps
See when I was looking Extang was the only company that offered this option.