I just noticed the thread.
Box vans are a special case. Attempting to teardrop them compromises load volume. The advantage the box van has is length, or fineness ratio. The long flat sides and top allow opportunity for disruptions caused by the nose mirrors and trailer gap to reattach so you have — I forget what — between laminar and turbulent flow. Attached turbulent? Anyway here's a diagram that maps out areas of opportunity:
I wish I had a picture of the truck I saw downtown today. The aerocap on top the cab
was shaped like a dolphin's forehead and the visor was a free-standing wing. Ultimately though you want your cab to look like this:
