I used to store a bunch of hard drives with ZFS snapshots of my stuff in the garage. Not ideal, but better than nothing, and it’s technically a separate building lol
I only have roughly 5TB of data though.
Definitely looking to improve the situation, cause at the moment I have no offsite backups at all :/
This does sound interesting! Would need some tooling to lay my paranoia to rest though, and some trust towards the other person.