Grizzly,
Dually Depot has these tanks made for them & they install them in Elkhart, IN. The one I have was their largest tank and their cheapest due to the shear volume of tanks sold to the trailer haulers. Those guys wanted as much holding capacity as possible.
I do not know if they have one with a tool box attached. What about installing a separate tool box? Not enough room, I imagine. However, the extra fuel capacity where the tool box would be on top of the tank might come in handy. Just a thought.
In the event you're interested, Dually Depot's number is 574-266-9151 & their email address is duallydepot.com. Hope this helps.
Joe F.