That is one of the old "coffin" type sleepers normally used on road tractors of the day. Capacity one wide and two deep (ask my ex-wife)
. There is every reason to suspect my oldest son was concieved in the sleeper of a Freightliner in West Memphis Ark during a blizzard.
There is no way you could sleep in that thing going down the road.....it would beat your teeth out.
Normally you crawled into them through a small hole in the back of the cab.
It's possible they may have converted that one with a bench seat in it to haul more than the normal three man capacity of a duece.
They could have taken the bed off of a long bed duece, added the sleeper and put a regular size bed on it.
It's a red headed step child for sure.