You could use one of the zero-knowledge file sync services that exist online. Examples would be http://www.spideroak.com, https://www.boxcryptor.com/en and so on. Pick any one that earns your trust.
Basically, they offer a Dropbox-like service, but they promise to encrypt all your files locally, on your own machine, using a password that never leaves your computer, before the files are uploaded to their servers.
Of course you'll never be completely sure that these services don't have a backdoor somewhere in their software, but that's the price of using a finished product, instead of rolling your own.
https://librevault.com/ might be a way to go if you want to inspect source code to make sure there's no backdoors, but it doesn't look like it's ready for prime time yet. Maybe there's other zero-knowledge open-source solutions around. If there were, I'd favour one of these.