Not my solution, but I liked an idea and thinking to use it too - copy backups on external HDD and put it into your car trunk. Maybe have two drives in rotation.
It eliminates a need to drive somewhere for rotation, and any cost of renting a safebox.
Doesn't protect from a serious disaster like forest fire or earthquake or nuclear war, but I keep the most important data in cloud, and if my house and car burns I would be having other problems than worrying about some homelab snapshots.