The great things about short buses are that they usually seat less than 15 so there are no extra DL requirements and they usually have a van nose so they can be registered and insured as a 1 ton van. My insurance agent knows exactly what it is and had no problem with this.
On a side note, the only reason I didn't register mine as an RV is that I pull a stock car with it so the State Patrol considers it a commercial motor vehicle. In MN you cannot pull a commercial motor vehicle with a truck licensed as an RV, even a motorhome. You have to license it as a truck. Very stupid rules. Just something to think of if you plan to use it for anything other than an RV. Calling a State Patrol scale would yield you a lot of more useful information than calling the DMV.