I'm in a similar position. I dualboot and have a truecrypt volume I share between Linux mint and Win7. Works great.

Maybe EncFS [0]? Its Windows port is experimental, alas. I suppose it would be suitable if you were willing to make frequent backups.

[0]: https://en.wikipedia.org/wiki/EncFS

There is a relatively recent audit[1] of EncFS with some damning results. I really wouldn't use it.

[1]: https://defuse.ca/audits/encfs.htm

> damning results

They didn't seem that severe to me, they seemed pretty minor actually. Especially if your attack vector is solely a read attack rather than a read-write attack.

Which one got you worried?

> EncFS is probably safe as long as the adversary only gets one copy of the ciphertext and nothing more. EncFS is not safe if the adversary has the opportunity to see two or more snapshots of the ciphertext at different times. EncFS attempts to protect files from malicious modification, but there are serious problems with this feature.

Which, seeing as my current major use case is to lock down Dropbox, kind of renders it useless for me.

EncFS is horrible.

However you should not use XTS with Dropbox http://sockpuppet.org/blog/2014/04/30/you-dont-want-xts/