If you look closely, you can see that the front of the tub has at least been removed and replaced with a pole running from side to side. I imagine you'd fold down the front seats, remove the pole, and sleep front to back. Just a guess. I'd also imagine that you'd have to be about 5'5" tall to make this workable, and have a high tolerance for uneven sleeping surfaces.
The big advantage is that all of your weight is down low, so you aren't much worse off than stock configuration on sidehills.
The problem I see with this sort of sleeping arrangement is that you have to unload all of the cargo out of the back every night, instead of just popping the top and crawling in (like a Dormobile, X-Panda Cab, or RTT).
I'm playing around with building mounts for a shortened military stretcher. It would run from the dash to the rear of the tub on one side, providing sleeping space for one. I was also looking at fabbing up my own version of the X-Panda Cab. However, I may just get a good RTT and be done with it.
Then again, I'm a long way from that stage of my project.