We saw a bunch of those out west when we were driving through the national parks w/ my family...
Our theory was that it was a tour bus, where you could sleep in the back , or sit up front... (they seemed to be asian or european tourists)... maybe some kind of budget tour?
David-S: that's what it looks like to me. In all honesty, I'd be inclined to let the folks go to the back to sleep and I'd just sprawl out across the seats. Of course without actually seeing the interior I can't say for certain, but the sleeping quarters don't seem particularly comfortable.