Disclaimer: The materials provided below are informational and should not be relied upon as legal advice.
You certainly should document the outstanding balances with a properly drafted promissory note and security agreement. UCC Financing Statements typically are not used against motor vehicles (except perhaps motor vehicle inventory sitting in a dealership lot). Motor vehicles are governed by the various Certificate of Title Acts in the various U.S. jurisdictions, so the creditor's lien should be noted on the vehicle's title by that jurisdiction's DMV. You should consult your own attorney to protect your legal rights.