We have a distro, Lubuntu 16.04, which we want to pack with a concrete SW, ToolboX (util/deb/toolbox_1.0-1.deb will install Geany, LaTeX packages, GNU Octave, etc., some extra 1.2GB, overall). Now, we have a functional installation and want to produce a persistent live version out of it, so that users (children, mostly without Linux knowledge) can easily burn a USB stick and start using it, keeping track of WIFI password and local files.
First thing I've tried is to produce an ISO with systemback, which works nicely after been copied (dd) to an USB stick. Problem is that systemback won't add persistence. Following these instructions, I've tried to add persistence to the stick, but it fails for some reason (it works well with an original Lubuntu ISO, but doesn't work for the ISO generated by systemback). Even if it would, this produces the stick itself, but the goal is to have an ISO that, when copied, provides a persistent version of the customized distro.
What are the alternatives out there to end up with this ISO?