More machining - I finished the two walls.
Gas Sensor Base: This was all done by the laser cutter. The second try went much better than the first because I worked with a bigger piece of Plexiglas that allowed the machine more leeway to zero imprecisely.
After soldering everything together, I have to fix the gas sensors to the base I just machined. The gas sensors go into these little 7-pin vacuum tube sockets, which then sits snugly in the little holes on the base. I then solder the wires of the gas sensors onto the solderable breadboard and screw in some standoffs to create a small unit:
This will be later attached to the top of the box, on which we will install all of the other sensors. The four free wires are the data wires that will be connected to the Arduino.