@anisgh Don’t think there is any way you can automate this using FOG as it is right now.
It might be possible to use pre-deployment scripting to setup LUKS encryption on the device and then deploy the image to the encrypted LUKS containers on disk. But I am sure there is a lot you need to fiddle with to get this going. Give it a try and keep us posted.
Post deployment encryption is not that much an option I find. While this can be done on Windows (VeraCrypt or Bitlocker) I have not found a good way to do this on an already installed Linux system yet.