The truck looks to be a 10,000 gvw cutaway with a supreme box...no logs or scaling required, that starts at 10,001 lbs BUT, it also looks to be a heavy aluminum sided box and no "air dam" on the roof of the cab. Chances are the mileage would be in the 9-12 mpg.
There are all kinds of these doing expedite, most being used yellow penske trucks.....you can make them work, but after you load them up with a sleeper and personal stuff, chances are you will end up with less then 2500 lbs of available payload.
will it works? Yeap..Would I do use it? Nope....based on the above and then the maintainance cost of the 6 tires, larger brakes and suspention components.....
If a "cube" is what you are considering, look at the used srw 12-14 ft box units...most are of the older units are 9600 gvw , while the new chevy / gmc are 9900 gvw....