The solution to that is to use a Disk Utility sparse bundle disk image.
The only issue I can see is that you might have to reupload the entire disk image file whenever you make a change.
So, why can't you just store the TrueCrypt file in the Dropbox folder? Each time you make a change to the mounted disk image, the TrueCrypt file changes will be uploaded. I'm guessing you have more sensitive requirements though? So, if you want encryption that only you can access with a password, then something like TrueCrypt, or simply, an encrypted Disk Utility, disk image is what you want. subpoenas), and, of course, the data stored locally is not encrypted. The caveats to the above are that Dropbox employees can decrypt your data (if necessary e.g. First of all, Dropbox is encrypted both in transit and in the storage in the cloud.
