Losing your repository loses everyone's access at once, which makes it a bigger risk than any individual lost key. Backing it up is easy because it contains no plaintext:
Run that to two or three independent places on a schedule. doctor reports how old your newest mirror is.
Backups are not secret, but they are not harmless either
There is no plaintext in the repository, so a leaked backup exposes no values. It does expose structure: who your members are, what your vaults and secrets are called. Treat backups as confidential, just not as catastrophic.
Two habits that turn a plan into a working plan:
Restore drill. Actually restore from a mirror into a scratch directory and run secretsmgr verify. The restore also gets compared against what your clients have already seen, so a stale backup is caught as such rather than quietly rolling you back in time.
Recovery rehearsal. Pretend someone lost their key, and run the lost-key chapter end to end. Fifteen minutes now, versus improvising it during an incident.
doctor tracks the date of both and complains when they get stale.