If you are getting a per diem for the hotel, use it, a good night's rest will make you a happier person. I don't know about you, but sleeping in a bed, taking a hot shower and taking a dump in private are the basics to me. It is hard to put a price on that.
+1 but I understand where your coming from Ken. biggest thing your gonna need is insulation, roof, floor, walls, back and side doors. for the floor I would suggest building a floor from wood and insulting under it.
wall unit air conditioner or roof top rv unit will take care of heating and cooling.
your also gone need some shag carpeting, christmas lights on the ceiling, mirrors and hams beer signs for some ambiance.
better yet, just buy yourself an RV, if it has a bathroom, its a tax write-off like a house, and you can using it for camping and fishing trips as well. even a pop up camper behind your van would be better.
oh and, just know if your anywhere near me you will get locked in that motherfucker at night so it better have a bathroom.