Joseph shows off a unit just built at Harbor Truck Bodies. This one is a Low-Pro Harbor WorkMaster on a single rear wheel E350 Cutaway Chassis. The Cutaway chassis has a number of advantages. First, it is lower to the ground because of the way the frame is designed. Second, this one has a very similar wheelbase to that of an 8' pickup truck, and yet this has a 10' body. This means that you can have about the same footprint, but carry much more cargo.
With the Low-Pro body, this allows entrance to almost anywhere that a regular cargo van can go, and yet, again, this has a lot of storage for parts, tools, and other equipment.
See more about the Harbor WorkMaster at http://www.htbi.net.