Locking fuel tank tops

Back in the late '70s I paid $65 for a old Ford to drive home from terminal so did not need to leave anything nice parked in the lot for weeks at a time. Came in once, did not have enough gas in it to get to station. Was late fall, time for me to drain some fuel out of Pete tanks to reduce chance lines freezing. To solve the theft issue, I put a Derby fuel tank in the trunk. But because cars of that era drove so much better in snow with a full tank I decided to store that wet diesel in the car's tank. Next time I got to town a dispatcher was holding up drivers so he could witch about how much it cost to clean out fuel system on his fancy car. I checked the gas gauge, walked back in, reached across the counter and busted his nose. When I told the drivers why, dispatcher did not even clean out his desk.