I wrote an email to the VT DMV asking what the requirements would be to get my conversion registered as a motorhome. Here's the response I got today:
Thank you for your inquiry. 32 VSA §8902 (11) defines a “motor Home” as:
A new or used pleasure car designed to provide temporary living quarters, built into as an integral part of, or permanently attached to, a self-propelled motor vehicle chassis or van. The vehicle must contain at least four of the following facilities: cooking, refrigeration or ice box, self-contained toilet, heating and/or air conditioning, a portable water supply system including a sink and faucet, separate 110-125 volt electrical power supply, and/or an LP gas supply
In order to convert the bus into a motor home you must have at least four of the facilities listed in the definition. If you do that the bus will be able to be registered as a motorhome. I hope this helps."
Being that this list does not include a bed, I think I need to re-prioritize. Also, you may have guessed that this is very much a "grow as you go" operation, so I'll be putting together systems in as minimal a fashion as I think I can get away with, just to get the rig registered. The bus already has heat and A/C; a big cooler should be adequate for an ice-box; I'll need to buy an inverter/charger once I get my batteries in order to fulfill the 110-125V requirement (or maybe I'll just borrow someone else's to pass inspection); and my sawdust toilet system should be enough to finish off the fourth requirement. Maybe I'll hook a camp stove up to the empty LP can I got with the bus, just for good measure.
After all that I'll get back to this bed contraption.