The only thing I'm really worried about is the "extended bunk over cab" concept. None of the major vendors are doing that, and I'm thinking there's gotta be a reason for that which I'm not aware of yet.
Here's a typical Showhauler with a good view of an overhead bunk:
So...basically, is this design workable? Anything obviously wrong? "Blueprint" done in Windows Paint so don't laugh too hard...I ended up doing my own scaling ruler.