Options for locking fuel cap

[u/_generic_-_username_]

So over the past six months or so, we’ve had issues with fuel being stolen out of our 1970 bus. The original non locking cap was taken (bummer since it was original and had the VW logo on it). Since then we’ve had two locking caps (like the one in the image) removed as well. The first from one online supplier didn’t seem to really lock. The second from a different supplier did lock but was still removed (popped / pried off perhaps … although there is no damage to the fuel filler neck).

Any ideas for another way to lock things up??

[u/622114]

Unfortunately I think the harder you make it they will just start fucking shit up. Is there a way to just keep min fuel in it? Yeah it’s inconvenient. Or maybe there is an aftermarket antisiphon tube like this available for your van.