We have one of the side tent beds that you bolt into the side of the trailer and it folds out. It would be great in a cargo trailer conversion.
Not what you are looking for but you may get an idea from it. http://www.livinlite.com/18sut-overview.php
Have you thought about building your own? using the forum here and watching guys build their own has given me ideas on what I really need. Good luck!
I use an 11' x 11' tent at the of rear of my trailer.
The last trip in July I stayed at a real campground and had water sewer and electric.
I used a large shower base and a portable toilet, set up behind a shower curtain. The trailer sat on a gravel base, so no real issue just dumping a gallon or so of water out on the ground. I use an L-5 hot water heater. The tent does support a woodstove as well.