Changing a registration from bus to RV in many states has actually gotten easier than it used to be, at least by the accounts I've read and my personal experience.
Usually you just need X number of house features out of a list they provide. Things like toilet, cooking appliance, beds, food storage, etc. Get the list from your state, install the required number of house features, and then get any necessary inspections to verify.
In some states, like Wisconsin, no inspection is needed. You just fill out the form to change registration and they'll change your title. When you do this they read you a big warning that if you're stopped by a trooper and the vehicle is found to be registered incorrectly you'll receive a hefty fine.
In other states, you have to have a trooper inspect to verify that the required changes have been made. He/she then signs off on the form. Once that is done you submit, pay the fee, and get the registration changed.
If you research this and find out what's required, then do what's required, it's not that big of a deal.
One big caveat - if you go to the DMV and get a black stare, stop the conversation. You're not going to get anywhere if the person doesn't know what you're talking about. Politely ask to speak to a supervisor or someone that knows the specifics about changing a registration type.
Once the registration is changed, I agree with the earlier posts. Never mention the word 'bus' to either the DMV or your insurance company when talking about your motor home. Once the registration is changed, it becomes a motor home and stops being a bus. Use the word 'bus' and everyone gets freaked out.
