The only solution, as far as I see it, is using encfs with cryptkeeper(GUI),
just "apt-get install cryptkeeper" and use either the GUI or the encfs (man
encfs). You should place the encrypted folder in dropbox and the mount point
elsewhere.
From cli should look like this:
encfs ~/Dropbox/.crypt ~/crypt #for mounting/creating
fusermount -u ~/crypt #for unmounting
If uploading the whole container is ok for you (since you used truecrypt) you
can try using a luks container; it would be something like:
dd if=/dev/zero of=/luksfile bs=1M count=2100
losetup /dev/loop0 /luksfile
cryptsetup -c aes-xts-essiv:sha256 -y -s 512 luksFormat /dev/loop0
cryptsetup luksOpen /dev/loop0 crypt
cryptsetup status crypt
mkfs.xfs /dev/mapper/crypt
mount -t xfs /dev/mapper/crypt /mnt
chmod o=rwx /mnt
umount /mnt
cryptsetup luksClose crypt
losetup -d /dev/loop0 # free the loopdevice
mv /luksfile ~/Dropbox/luksfile
# For mounting you would use something like:
losetup /dev/loop0 ~/Dropbox/luksfile && cryptsetup luksOpen /dev/loop0 crypt
&& mount -t xfs /dev/mapper/crypt /your/desired/mountpoint
# For closing you would use something like:
umount /your/desired/mountpoint && cryptsetup luksClose crypt && losetup -d
/dev/loop0
