After playing around with using TrueCrypt and syncing the volume over Dropbox I was disappointed to discover that it doesn’t let you mount the volume by double clicking on the file. You have to open TrueCrypt, select the file and then type in your password.
To further expand my knowledge of OS X application bundles I set out to write an application that associated with the `.tc` file extension and when you opened a `.tc` file it would prompt your for your password and once you are done and eject the disk, automatically dismount the TrueCrypt volume.
The fruit of my labour is available in [this GitHub repository](https://github.com/samuelkadolph/TrueCrypt-Mounter) and you can download [the application here](https://github.com/downloads/samuelkadolph/TrueCrypt-Mounter/TrueCrypt%20Mounter%201.0.0.dmg).
Once you have copied the application to your `Applications` directory, it will associate with any `*.tc` file. You must add this extension to any of your TrueCrypt volumes because (unfortunately) TrueCrypt does not do this for you automatically.