Thanks for your answer. Using Truecrypt and saving it on Box.net or Dropbox was an idea I also had. This cheap solution only has the problem that anyone who gets access to my cloud hosting area could find that Truecrypt container if it isn't cleverly hidden or disguised. And that master password has to be very very long and very complex, as I learned from Ars Technica:

* http://arstechnica.com/security/2013/05/how-crackers-make-mi...

Therefore I'm more looking for a convenient online solution that still offers some safety due to two-factor authentication for example.