call GMAC insurance. Yes, they sell insurance. Tell them you have a bus and plan to convert it to a motorhome. I live in michigan, and have not yet titled my bus (after a year and a half) as a motor home. It's simply a non-commercial bus. GMAC will insure your bus with the code BUS C which i think stands for conversion. My insurance is about 50 bucks a month, but i'm 25, you're cost could be higher.
It took a long time for people at the michigan secretary of state (dmv for michigan) to figure out how to liscense the bus, since it was not a motorhome, but wasn't a commercial vehicle either. When all was said and done, registration was only 27 dollars for a year. I hope you have the same good fortune..
Quis custodiet ipsos custodes (who will watch the watchmen?)