I created my own locking gas cap by taking out one out the screws around the fill tube and running it from the inside of the trunk out. To unlock it you will have to open your trunk and unscrew the one screw from the inside to get your cap off. Once you put the screw through from the inside "finger tight" it will mark the inside of the gas cap for you. Tape a thick washer there and make sure it clears everything, then Epoxy it at that spot. Or cut a semi circular piece of metal that will fit inside the inside of your stock gas cap around the edge and use the two handle screws on the inside of the cap to attach. Then drill a hole were the locking screw protrudes. You will want to grind the end of the screw's point off. You may be able to find a screw at ACE hardware with a wing nut head. This is effective and it keeps the stock look of your car. I doubt even a car show judge would catch it.