I'd like to set a single directory inside Dropbox in which files are encrypted on a file-by-file basis.

At the moment, I use a 2Mb Truecrypt container inside my Dropbox which I then have to mount manually, access/change the files within, then unmount manually. At that point, the entire 2Mb uploads to Dropbox. This is a pain for a number of reasons :

1. Dropbox sync will only occur when the Truecrypt container is unmounted, because Dropbox only syncs files that aren't locked and mounting a container locks it.
2. A single byte change to one file inside that container results in the whole 2Mb being uploaded again.
3. It doesn't scale - I was originally using a 10Mb container, but obviously the bigger the container, the longer it takes to sync when it's unmounted.

I was wondering if I can somehow use LUKS to implement file-by-file encryption to get round the "container" issues.