securely saving kmail critical info to an USB key

This is what I have done on my macosx system for this:
1. created a directory for what I deem to be critical files (emails and configuration) on my system:
~$ md /<path-to-mail-backup-dir>/mail-backup
2. created a script able to update the backup directory, from the major ~/.kde place, tar and encrypt (using openssl and a password file to [...]