As Matt says, I’ve already implemented this in 1.5 (out early next year). There is a “Backups” preference pane especially for this, which allows you to choose a backups folder, whether backups should be saved at specific time intervals or on project open or close, and whether they get zipped up or not. (No password protection, though, I’m afraid; I looked into adding it, but there’s no straightforward way when using the commandline tool which Scrivener uses in the background).
All the best,
Keith