Below are the Oklahoma tax commission requirements for title change from School Bus to RV.
OAC 710:60 OKLAHOMA TAX COMMISSION
(4) Recreational vehicles. "Recreational vehicle" means every vehicle which is built on or permanently attached to a self-propelled motor chassis or chassis cab which becomes an integral part of the completed vehicle and is capable of being operated on the highways. In order to qualify as a recreational vehicle pursuant to this subsection such vehicle shall be permanently constructed and equipped for human habitation, having its own sleeping and kitchen facilities, including permanently affixed cooking facilities, water tanks and holding tank with permanent toilet facilities. Recreational vehicle shall not include manufactured homes or any vehicle with portable sleeping, toilet and kitchen facilities which are designed
to be removed from such vehicle.
They also require a Body Change Affidavit form be filled out https://www.ok.gov/tax/documents/701-9.pdf