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. An Illinois motor vehicle bill of sale documents the purchase and sale of a motor vehicle between a private seller and buyer in the State of Illinois.Get the buyer, seller, and witnesses to sign the bill. At the bottom of the form, leave spaces for the buyer's and seller's signatures. Prepare a bill of sale for the buyer. Include the date of sale and the price paid. Registering a trailer in Illinois does not require an Illinois trailer bill of sale, but you should have one when you sell or buy a trailer. All Municipal, County, and State taxes in relation to purchase of the motor vehicle, including sales taxes, are included in the purchase price.