Hello!
I'm a new kid on the block here with a 1960 Minor called Happy. Well, you can call me happy. So that's what I call her right now. I put an intro in the Where are you from? thread.
Now, I'll take a risk that it may be unlikely thieves are reading this site. On the other hand... it may be wise to not release too much public information on location. Hmmm.
At any rate... I have a camper van (1987 Ford E150 with all the works, like a Westphalia would have but, well, bigger).
I use it for camping and hiking and am often parked in the boonies. Will need to get a locking gas cap because gas for it, as is for Minors, is a target for theft. The parking spots out in the wilderness areas are targets for vandalism and getting away with it, often with valuables because of traveling. I'd hate to be stuck miles from a real road... argh, with everything gone or trashed. No cell range, etc.
Anyways, on the van, I asked a mechanic to run a hidden "kill switch toggle" in a location I can reach but unseen and only I know about. It simply cuts out any juice between the ignition and the battery. A person may still be able to hot wire it I suppose but they would have to be very motivated and with time on their hands. Most thieves are hit and run types.
The toggle is great because I know that if someone jumped in, had those sets of keys thieves use, nuttin, not even a starter click.

Cheap for a mechanic to install or a do it yourself project with basic wiring skills.
This has has been an eyeopening thread to read. My former '58 was broken into and small items stolen. A car theft, though, how heart breaking. Thank you folks for sharing the reality of metal thefts etc. In my area it's copper wiring even at great personal risk with high voltage boxes for public utilities. Meth money is the usual motivation. Sad.
Am reading a book looking at the criminal mind. Basic gist is they do it because they can. Just like we love Morris' and we enjoy the time spent and camaraderie, same goes for people who like to thieve or hurt others... etc. Interesting view but I digress. Main point being, sort of like why climb the mountain/steal a Morris? To some, it's because it's there and the easier the better.
Be well, and may all be safe, cars and their humans included. Try the toggle! Let us know how it works for you. Gotta remember to use it, it's always optional. Oh, and let others know who share the car.
StinkBug. (aka Kathryn)