you need this, I believe there is also a locking one available
http://cgi.ebay.com/ebaymotors/dodge-challenger-gas-cap-70-under-flip-top-free-ship-_W0QQcmdZViewItemQQhashZitem35ad60e99bQQitemZ230542076315QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories