I'm on Mavericks (10.9.5). I have an external USB drive that I use exclusively for Time Machine backups.

I just realized that the backups are unencrypted. Is there a way to configure Time Machine to encrypt all backups on this drive, both existing backups and future backups, without erasing the existing backups?

This answer indicates that it can be done with "sparsebundles", but the post is 5 years old and it seems risky.

Is there an easier way?