Encyption of thunderbird data?

Is there a way to encypt the thunderbird folder whilst still retain the portablity of it.

If so what would be the best thing to use?

I like the idea of having my email & client on my flashdrive so I can use a full featured client instead of relying on webmail, also being able to re-read emails offline is usefull, however im a bit concerned should i lose my flashdrive someone could find it and read the emails
Which is why id like to use some form of encyption/password protection if possible.