Thanks for this article on rdiff-backup and sshfs.  I'm already a fan of both but hadn't thought of using them together.

A note on installing sshfs on Debian (and maybe other distrols) that isn't mentioned in the docs or on the program's FAQ.  Your user account must be a member of the fuse group or you'll get

fusermount: failed to open /dev/fuse: Permission denied

So, do:

sudo adduser <username> fuse

newgrp fuse

sudo adduser <username> fuse

newgrp fuse