For personal backup of key files (not endless GBs of movies, just documents and precious pictures) I usually sync a Sparse Disk Bundle[1] with a good AES key. Sure, you have to trust Apple's AES implementation (I don't to any great extent) but it gets you some degree of privacy without much hassle. It is a cheap insurance policy.
I wrote a FUSE filesystem (https://github.com/netheril96/securefs) to secure the data that is meant to be synced to the cloud. In principle it is more secure than alternatives because the randomization and authentication of encryption. It encrypts file by file so that no need to sync a huge data when you only change a single file.
I see you submitted this a while back, it's a shame there wasn't much discussion! Seems like a neat idea and (to my naive knowledge of cryptography) a solid implementation.
[1] https://en.m.wikipedia.org/wiki/Sparse_image . It uses 8MB chunks by default which sync quite quickly.