http://h7isucmawckzflxhipflydxvxpaytk5fozfk5immffg66rhboc74yxyd.onion/doku.php?id=backups&do=edit
Because USB keys are cheap, this is a simple, cost effective, mitigation.
You might want to attach a keyring to the USB key, with the name of your machine on it, so that you remember that that USB key is your backup key.
If you want to make things easier for yourself, you could write a small script to copy across the files that you want automatically.