According to the info I have on hand currently,
a Sprinter's interior length states: 121" or 161" or 177".
So as bigger is always better in C/V Expediting... take
177"-156"(4'x3=12', plus 12" extra) = 21"
So it might look like 21" is all that is left for a
"fixed type sleeper"...
Basing...