Someone's already done & blogged about this, using multiple free FTP accounts, with a FTPfs bringing them local, then mounting a RAID (mirrored & parity) partition over it, and encfs over the top of that.
It was VERY SLOW, but did work, even when he blocked access to some of the FTP accounts - it was just seen as a failed drive read, and the parity reconstruction still permitted access.
I think the key problem was that FTP servers he used (or the FTPfs driver) didn't allow for partial writes to files, so every time you changed something, large amounts of data was re-uploaded. So there were possibilities for optimization.....
Enjoy & share if you get anywhere !
Dom