Sprinter vans are unique in that they are "unibody" BUT also have a box frame "backbone" which is integral (hence the unibody label) with the body structure and use the floor sheet metal to complete its 4 sided box member.
This "frame" or "backbone" is actually available as a separate part number for repair purposes but I suspect a body repair facility would only need to use potions of it for partial cuts/repairs. Imagine the number of spot-welds to "free". Doktor A