Hi Guy! I subcontract for an art handling company in the Bay Area that owns a Sprinter, a Transit, and a box truck, with both the Sprinter and Transit being modified on the inside with plywood and E-Track. The Sprinter has a tighter turning radius, and is the one the guys all want if we're doing any jobs in the city. They are both tall, however, (~75" interior height) which is necessary on the one hand to transport over-size artwork, but sometimes causes problems when looking for parking. For your application, I highly recommend buying a Sprinter, modifying it as needed, and lining the floor with 1" ethafoam. Then when you're transporting dirty items just remove the foam for the day and you can sweep out the van once you're done, and replace the foam for the next day.

I don't have any direct experience with leasing a vehicle, but I imagine there are limitations to the modifying you can get away with under a lease agreement.
Thanks for starting the thread!