That's why I was writing about a "messenger" specifically. I was thinking about someone you can trust, if need be, yourself. If this messenger assures you the key wasn't spied upon, you can use the key. If you can't even get a courier with a sealed envelope to the location, then you probably won't get any encrypted or otherwise protected data in there, anyway.

This level of security is ridiculous for almost everyone, of course. But we are talking about a self destructing SSD, which you want to send via courier to initiate the destruct, as an alternative. So I think this is a fair comparison.