Clearly print or type all information, except signatures. The proof of sale for a vehicle from a dealer is the Retail Certificate of Sale (MV-50) ("Dealer's Bill of Sale").An RV Bill of Sale is a legal document that serves as proof of the sale and transfer of ownership of a recreational vehicle (RV) from a seller to a buyer. This is typically one of the first items you'll put on the bill of sale. A Recreational Vehicle (RV) Bill of Sale is required anytime an RV is sold or transferred between a seller and a buyer.