Here's one that I posted a while back, still had the pic saved... if you could get a pass thru, I see no reason why you couldn't build a stand up, wide body sleeper, and still have the required cargo room.
The only problem would be, the weight of that box.
It would depend on your company .. and how much they require you to be able to haul. For instance, some companies require 3000 pound capacity for van load if I remember correctly. Therefore, if you built a sleeper into this box, you wouldn't be able to haul a required van load, as the Payload is only 3100 ... as it is. Ad in the weight of plywood, bed, etc, you'd be too heavy. I believe some companies only require 2000 pounds capacity tho.
In contrast, I'd like to see a regular 3500 (dual wheel Sprinter) with the wheel wells modified to allow normal skids to fit. The second pic is what I'm talking about here.. It would still have the 9,990 GVR, but without the heavy weight of the box. Still have a standup sleeper, but haul more weight than a similarly equipped SINGLE wheel version, or 2500 series Sprinter.
Dreamer
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NEW 2004 FREIGHTLINER SPRINTER C3500SHC, 5 Cylinder Diesel Mercedes 154 HP, 5 Speed MB Automatic, 158" WB, Roll up Door, White, 14' Cube Van, 9,990# GVWR, 3,100# Payload, Step Bumper, AC, Cruise, AM/FM/Cassette, Rated 20+ MPG,