Its not that unusual of a floor plan, I ran across several when I was shopping around the last few years. I haven't seen any newer than about a 2004 or so, so I don't believe they were produced very long. I think this is the floor plan;
The bed is kind of on the narrow side and there were not any rails or anything of the like in any of the ones that I remember looking at. I wasn't real comfortable with the set up with the bed that far off the floor, and besides, I was pretty dead set on finding a 3 bunk unit. I cant remember the arrangement exactly, but I wouldn't think it would be too tough to build on to it and extend it up, but Im not sure what to do about the window being there.