Robgoss, please see my reply to your older post - Installing Systemback
Shortly after I posted that answer, I downloaded and used Systemback to create a complete .iso of my MATE 18.04 installation on my old D830 laptop. I tested the .iso and sure enough it performed as expected in a reinstallation. See - Using Systemback for details for using this utility.
I’m also a fan of Clonezilla if that matters. Good luck Rob.