Help me with a rotating firesafe data backup

I have between 20-30 TB of data I want to keep a copy of in a firesafe. I do not want to use an online storage solution, I want to maintain my personal data at my home.

My current plan is to get (2) Mediasonic HFR2-SU3S2 PRORAID enclosures and (8) WD Red Pro NAS 16TB drives to fill them. The first would contain a full backup and be placed in the safe. The second would be attached to my machine and receive nightly backups. Periodically, I would rotate the enclosures, taking the one from the safe and swap it with the one connected to my machine.

Are there any problems with my plan that I am not thinking of? Are there better solutions?

Is anyone else keeping a rotating data backup in a safe? How is it working out for you?