Would you ever consider building a camper off of that box, I.E. using that as a starting point? What do you think the box construction and mounting is?
I'd say 100% yes. That is what I am doing (mine is a Marathon box, that is a Supreme, but the construction is the same).
.040 aluminum rivited to stringers every 16 inches. Rivited aluminum skin has been used since pre-WWII on aircraft that go through 100,000+ cycles without problems. Also these commerical boxes have to hold up to maybe a million+ miles, so if they can handle that, they can handle some 'market roads'. Very easy to run wiring, easy to insulate, etc, etc.
Yup, change the frame U-bolt mounts to a simple 'spring type' and you would be good to go.
Beside a 'box truck' is a pretty safe bet, just running around town, not pushing a snow plow or living its life as a dump truck like so many FGs do/did.
And it is a 2007, the last of the pre-DPF trucks, highest HP/torque Fusos, with pretty low mileage. The perfect (well as perfect as a FG can be) starting point, IMO.
I'd be on it like my dog to an unguarded ham sandwich if I did not already have mine.