No worries. If the key is not something known by anyone other than the relevant parties and is not stored or transmitted electronically then you’ve got yourself a pretty robust system.
It’s fairly trivial to set up your email client to send and receive encrypted email using PGP if you feel so inclined: http://arstechnica.com/security/2013/06/encrypted-e-mail-how-much-annoyance-will-you-tolerate-to-keep-the-nsa-away/
FWIW: In my opinion it’s silly to lock up artistic creation in any way. It’s easy to imagine a situation where your future relatives stumble upon something you’ve made and are unable to view or listen to it because it’s locked up and the only people who knew the key are long dead. If you’re not doing anything illegal or stuff that won’t raise the suspicions of the TLAs then save yourself, your friends and your potential future relatives the PITA of encryption.
