Why would he have to do that?
Did you not read where he said these 10 machines have no internet access at all?
If he could get LXQt installed it should run just fine. He doesn't have to worry about updates, or network vulnerabilities or being hacked, because he has only a local network (or maybe no network what so ever).
Maybe he runs his own package server in-house? Maybe its a school Computer Lab setting and internet access is not allowed? There are many scenarios where people run computers with no internet access at all.
Note: I also disregard a lot of the fear-mongering about having to apply updates the instant they come out. A rolling release does not have to continuously roll. If it was good enough to put out an official ISO image it should work just fine off of that ISO image for years and years in an off-internet environment. If you can make a case why that CAN'T work, then perhaps Manjaro should never make any ISO again, and move entirely to Net Install ONLY.
I do agree that this is where a net edition is the wrong choice and a full installer CDRom/DVD would be a better choice. Unfortunately Manjaro Devs can't make a complete ISO for every spin.
This thread is discussing only your net install.
Perhaps there is a full install image for LXQt somewhere that is not mentioned in this thread. I looked HERE but couldn't find it by name. The actual LXQt Download link on the community editions page takes you to a place that doesn't even have any file with LXQt in its name?!!!?
(Finding anything on the Manjaro Community Spins is always a hit or miss adventure. The whole sourceforge site needs a fresh coat of bulldozer IMHO).
The @eugen-b solution may also work by just mirroring the entire Manjaro main repositories on a small computer (RaspberryPi) which gets updated when an internet connection is available, and carried to the other machines (or a local only network) as needed. Sort of a Slow Rolling Portable Repository).