Have you tried: https://help.ubuntu.com/community/FullDiskEncryptionHowto
http://dailyanarchist.com/2012/02/20/full-disk-encryption-for-ubuntu-and-fedora/ http://www.linuxbsdos.com/2014/01/16/manual-full-disk-encryption-setup-guide-for-ubuntu-13-10-linux-mint-16/You don't need to switch between those distributions because almost all of them use the same tools. Moreover, Trisquel and Ubuntu share the same root: Debian.
