I have yet to try this install and so can not vouch for its’ workability. However, if I was going to install Systemback on UM 18.04, here is where I’d begin. Please see - http://www.francoconidi.it/systemback-1-9-3-per-debian-9-ubuntu-17-10-18-04/ which is written in Italian which I barely, if at all, comprehend.
His page leads to a dropbox page - https://www.dropbox.com/s/6mw0crupd7e2jfr/systemback-install_pack-1.9.3.tar.xz?dl=0 and from there you can download systemback for ubuntu 18.04.
He includes instructions for the install if you need them. Good luck @Robgoss.