I live in an '85 Grumman step-van I converted. It has a 14' box and is pretty skookum. It's SUPER easy to work on (one of the bonuses of being designed for commercial use) and I could remove the tranny without leaving the vehicle by unbolting the floor! Flat glass makes replacement a breeze, any window shop that sells safety glass can do it, and it's extremely roomy. I get between 7-8 mpg, but that's mostly because it runs on propane (doesn't have high compression heads/pistons to make up for the power loss), I've got a ton of weighty shit, and it has a TH400 tranny. It would be nice if it had a 4-5 speed manual in it, but wishes and fishes.
One thing I'm contemplating doing is swapping in a Detroit Tru-trac differential in the rear; 4 m&s tires hooking up in the rear would give unreal traction!
edit: I forgot to add that it's pretty stealthy, looking like a general contractor's vehicle.