For years, my wife and I and our kids have been talking about creating an underbay sleeping compartment in our bus conversion. Every time we took the bus out, the kids and their friends would love to clean out the belly of the bus, lay down a piece of foam and the sleeping bags, and sleep down below. The kids kept saying, "Dad, finish this off like the rest of the cabin." (We had a Moose Creek Motorcabin). Well, I kept talking about it, the kids kept asking, and finally, someone purchased our MCI 9 Motorcabin, with the condition that I finish off the underbay sleeping compartment. Isn't that the way it always goes: you do something to a house or bus in order to sell it, and miss the enjoyment of the finished project! So the job got done! With photos to prove it!
The compartment has a hatch under the dining table that allows entry to and from the compartment. Just lift up, and climb down (or up). Also in the lower cabin, I installed a TV, DVD, CD players, and stereo. The heat and A/C were ducted down from the vents above. I also placed windows on both sides. Look closely at the picture and you'll see how we fit them into the area where the rub rail is.
Another item to mention is where I placed a lever on the inside of each door, so the bay door can be opened from the inside of the upper compartment. The "lower bedroom" has 12volt reading light along with 12volt and llOvolt outlets for the kids to plug in their favorite games, toys, or curing irons. All four walls are covered with knotty pine to match the upper cabin. The plywood floor has carpet and padding which is not glued or nailed in, so it can be removed for easy cleaning. Or if the under-bay is to be used for hauling other things, not quite as clean as kids.
Now that that bus is gone, I'm building another to replace it. I have already installed the "belly bay" sleeping compartment. Interestingly, I think my wife and I will sleep downstairs. It is quiet down there, the kids can tear up the inside of the bus, and let us sleep!
A footnote: I'm confused as to what to call it. Downstairs Bedroom? Bus Belly? Basement Bedroom? Luggage Bay? Jail House?