Those bodies are neat! I've seen a couple camper build-outs using them, and they add just enough volume to seem it feel Sprinter-like inside, but with the durability of the E-series. Fuel economy should be at least as good as a stock body.
Note this one DOES have the TorqueShift option, since it's build on the cutaway chassis, which means it also has a full-float 7,800# rear axle since has the rear fuel tank as well.
2000 E450 dually V10 wagon