I would suggest using restic over TarSnap for encrypted backups -- it gives you more flexibility with where your backups will be stored since TarSnap is pretty integrated with Colin Percival's online service and is also unfortunately not free software. But it's also an as-simple-as-possible cryptosystem. Filippo did a quick lookthrough and said that it seemed sane from a crypto perspective[1].
[1]: https://blog.filippo.io/restic-cryptography/