Right now 500 miles a day in anything is a dream.. Figure 1000-1500 a week. I just had a 400 mile week. Most sprinter owners I think sleep langth wise (IE head to the front, toes to the rear) sprinters are rather narrow.
The better question to ask, is WHO is signing sprinters. I know some of the better companies have stopped signing B units (although bigger than a cargo van, they are still B units).