Most of the time, we tow with toad door unlocked and chipped key in the ignition. No locks on the tow bar setup. Door unlocked is partly because our first toad behind our first coach, sometimes came out of a tight turn dragging the front wheels sideways instead of returned to center. Had to get out and crank the wheel over.
At least for the moment, I'm more concerned about the consequences of
1. Forgetting to unlock the wheel before towing...
2. Not being able to break the tow quickly because of locks on the bar...
... than I am of somebody trying to start the toad while we're in the rest room.
... for longer stops, I lock the toad door.
... and will try to get an un-chipped key copy made. Toyota that's chipped but not one of those laser cut keys. Should be do-able and cost-effective.
Oh, I am concerned about the vandalism "Let's pull these pins" issue. May have to consider some padlocks. They don't have to be anti-theft strong, just anti-tampering.