I went to one of the local auto parts stores intending to buy a locking gas cap. I was told that auto/truck manufacturers a few years back started building the fuel filler tube with a blocking device to prevent someone from siphoning fuel from the tank. Is this true or does anyone have information regarding this? They could not find a locking cap specifically for the Ford F53 chassis, so I'm curious as to whether they were just trying to ease my mind with their info regarding filler tube construction to prevent siphoning.