The backup tool itself doesn't need to know about encryption at all. I have full control over the backup host, so I would use either full-disk encryption (luks)

The backup tool itself doesn't need to know about encryption at all. I have full control over the backup host, so I would use either full-disk encryption (luks) or filesystem-level encryption (encfs/ecryptfs) on the backup host. The former works better if you want de-duplication. Regular ssh takes care of encryption in transit, so rsync just pipes unencrypted bits through this encrypted tunnel. You could probably add GPG in there somewhere if you wanted. Just a bunch of Unix tools doing Unixy things in the Unix way.