Backup the dropbox folder to the ubuntu one folder on startup. First backuo will be an encrypted full backup, after that it will be incremental.
install duplicity from the package manager
make this file in home directory and call it backup.sh. Make it executable
export PASSPHRASE=yourstrongpassphrasehere without spaces
duplicity /home/user/Dropbox file:///home/user/Ubuntu\ One/Dropbox
/etc/rc.local in your editor with root permission and add the command you want to execute at startup before the line
exit 0 in that file.
In this case it is
exec "/home/user/backup.sh" > /var/log/duplicity/logfile