Step 1: The DMV
It's not as bad as it sounds, however. Most of my research on this project suggests that few DMV personnel are familiar with the paperwork required to do this. So, having the relevant sections of your state's Motor Vehicle Code along with your forms when you appear at the window can really make things go smoothly. That said, I will share my experience in Florida in hopes that you can parallel them in your state.
Start by visiting your state's DMV website. You can find your state's official site listed at autotrader.com or at DMV.org. Once there, take advantage of their search engine, if they have one, to find forms and pages with terms like motor home, recreational vehicle, and conversion. My own efforts led me to Procedure TL-13: CERTIFICATE OF TITLE REQUIREMENTS FOR RECREATIONAL VEHICLES, MOBILE HOMES AND OFFICE TRAILERS. This was literally the hardest part of dealing with the state. Once I found this document, I was able to work with the local office to go step by step with them. A single paragraph covered everything I needed to know.
In the case of an individual converting their own vehicle and requesting to have the identity changed on the title in order to have it registered and licensed as a recreational vehicle, the customer must submit an affidavit to the tax collector. The affidavit must certify that the unit has been converted to the extent to include one of the aforementioned items to qualify it as a recreational vehicle.
This is to certify that I, John Doe, owner of a 1982 Thomas Transit Liner, VIN 1234 ABC 56789, hereby request the vehicle be classified as recreational vehicle for the following reason:
( ) Installed 110 volt electrical wiring
( ) Installed LP gas piping
( ) Installed plumbing system
That was it! I had the girl notarize it and do up the paperwork there at the window. $35 later, the bus was a legal motorhome. The 110 volt electrical wiring consisted of a four outlet electrical box mounted to the inside where I could plug in my work tools for the rest of the conversion. Now the vehicle could be insured and driven to the work site... which brings us to another important consideration....