You need a California Trailer Bill of Sale form to register your trailer with the DMV after purchasing it from a private party. 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.A Recreational Vehicle (RV) Bill of Sale is required anytime an RV is sold or transferred between a seller and a buyer. California Bill of Sale Forms (3). A California bill of sale is an official document used to record the sale of personal property between a buyer and seller. The California bill of sale form helps individuals document data on a transaction involving the sale, trade, or gift of personal property. If you are completing a bill of sale to satisfy a vehicle registration requirement, the law requires that you provide a copy to the DMV. What Is a Recreational Vehicle Bill of Sale? The RV (recreational vehicle) bill of sale form documents events related to the exchange of property between two compliant parties. How to get a trailer title with a bill of sale?