GPG keys are not that long, maybe 2 pages (ascii armored). Just print the private key out and store that in a safe or deposit box. You can physically see the key, so you know the backup worked.

If you ever need to restore it, yes it will take ~45 minutes to hand type the key back into a new computer. Oh well, that's the tax you pay for restoring your backup or making a new subkey.

Civilization has long figured out how to store paper. I've grown to respect how powerful a printer and some patience can be for key backups.

EDIT: I think most of the replies are missing the point. I want to keep things barebones. The only thing that should be required to recover is a copy of GPG. No qr decoder, script, or other nonsense. If you depend on something else for recovery, you are putting your trust in that. I trust GPG, paper, and my eyeballs.

Also: https://xkcd.com/1319/