Word of advice: you (in particular) will likely want to rename, let’s say one backup a month, to a name that Discourse won’t auto-delete when it reaches the maximum daily backups limit, and mirror that selected one elsewhere.
Just breaking the date format should suffice to avoid the auto-deletion (e.g. 2015-02-11 into 2015_Feb or something like that).
You’ll also be able to be a bit more lax in where you put the backups, because they’re encrypted and the private key is offline.
(Further explaining that: Backups contain all the private messages and drafts stored on the server! Which is why there’s a standard admonishment to not let non-admins get backups.)