Once you have the tunnels filled, it's not "airless"... just dark.
The inuit, inupiaq, and skraelings all also have biophysical adaptations to cold that most ethnic groups don't. (As un-PC as it is to say it, not all races are physically equal, and the Inupiaq prove it.) Ethnic inupiaq can work in temps to -15°C with their hands wet with salt water for periods exceeding 30 minutes without any form of hand protection, and without injury. Many can work for longer and in colder. White folk who try that tend to lose fingers.
TL4 manufacturing techniques include standardization and mass production. he materials used are suitable for same (lots of metals, lots of silicate stuff aka glass), and some polymers (acetate, celluloid, rubber, early vinyl esthers, Nylon, polyesther).
from the MGT rules:
TL 4: (Industrial) The transition to industrial revolution is complete,
bringing plastics, radio and other such inventions. Roughly
comparable to the late 19th/early 20th century.
TL 5: (Industrial) TL 5 brings widespread electrification, telecommunications
and internal combustion. At the high end of the
TL, atomics and primitive computing appear. Roughly on a par with
the mid–20th century.
We're talking full on electronics at TL 4. Pretty muh the full spectrum of lighting. Without internal combustion, however, we don't get to TL5... and essentially, IC is a BAD idea in a low-volume environment. The lack of petrochem is likely to slow it, as well; petrochem was a vibrant part of the TL4-5 transition on earth.
Silicone semiconductors, probably separate transitors, can be used for TTL computing for simple systems. Doping silicon isn't hard; geting it even enough for microcircuitry takes some skill.
These guys probably consider electricty their "hydraulic despotism" resource. Moisture will be a problem, because of too much, not too little.
Hmm.