UWS Had a couple nice options, I recall a 5th wheel box which was shaped like 5th wheel tailgate, the two side pieces had drawers and I think the middle section was bulk space. There were wheel well boxes too, that sat behind the wheel wells, it had doors you opened and trays that slid out.

Take a looks and see if anything is close, UWS Truck Accessories US - Storage Solutions, Drawer Slide Series