Without photos, it would be hard to say, although based on what you describe as soapstone (which is probably a ceramic humidifier) and the glass liner it could be about 70 years old, give or take. Glass liner = wartime materials shortage - humidors were often lined with copper or tin in the 30's and prior, but by the 40's, both tin and copper would have been scarce, if available at all due to the materials shortages. That is, if it is, in fact, an antique, rather than a more modern retro piece.
It also sounds like it was a personalized humidor either for or from someone possibly in or retired from the Royal Air Force (UK).
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