Forgive my inevitable naivety with regard to this sort of thing, but can't gparted create encrypted partitions, and why wouldn't that be secure enough...? My understanding is that it still takes a few hundred years to crack AES encryption with a standard PC... and the average criminals who are likely to blackmail you, I can't imagine they're well funded enough to buy a supercomputer sufficient to pop the lid on those things in a reasonably timely fashion.
Of course, if you piss off the Russian Mob, that's different, at least potentially... but that's also a comparatively pretty rare circumstance, I'd think.