My test chamber is nearly done. The main portion that I'm adding is a port to introduce precisely measured volumes of acetone (I can't drill the hole for it until I've re-checked my calculations).

I finally received my MQ138 sensor, it took a little longer than  expected due to few suppliers actually carrying it (Digikey, Mouser and Newark do not). In addition, it cost's considerably more than other commonly available gas sensors (instead of $5-10 it more like $40-50).

For my test chamber, I've completed the surround for insulation, heater pad on the bottom and finished all the wiring for the sensors, fan and heater.  All wiring ports are sealed with silicone.