You need Boxcrypotor installed. You need the sync software installed.
I sync through Google, Idrive, and Dropbox at work, home, and my laptop. I don't use it on "strange" PCs cause, well, then, that sort of blows the whole point of encrypting it. If you are willing to decrypt on a strange PC you are probably also willing to install the product(s) and do the same. When you sign out your data is encrypted and left behind but secure (or you uninstall and delete it all)