I recently started traveling a lot for work and I wanted a portable router. I had an old i386 netbook I wanted to use that would be perfect because it was tiny and had built in wifi, ethernet, battery backup, screen, keyboard, and mouse. I actually tried webmin first but couldn't get the actual router bit working, which is fine because I wanted to use Zentyal in order take advantage of all it's familiar GUI goodness.
Long story short what I did was first install Ubuntu Mate 18.04 and made sure it worked well and was fully updated. Next I added "deb
http://archive.zentyal.org/zentyal 5.1 main extra" to /etc/apt/sources.list and then ran "wget -O -
http://keys.zentyal.org/zentyal-6.2-packages.asc | apt-key add -" to add the repository key. Then all I did was "apt-update" and "apt-get install zentyal-network zentyal-core". That got the webmin up and running, and I just apt installed other zentyal modules as I needed them. Sure it's not the latest version of Zentyal and the configuration isn't exactly supported, but it works well enough for me.
Now all I do is use the netbook itself (or ssh and use nmcli) to connect to whatever wifi is available where I'm at and have all Zentyal features available to me. Normally I'm content to just plug my laptop in directly, but I also have a portable wifi AP if I want to connect other devices as well. I also have a T-Mobile hotspot that I use when there isn't wifi available.