I threw the PCB into a plastic project enclosure, and was surprised that it actually friction-fit pretty well. I lasered a thin strip of plastic to zip-tie the tubes to, and bent the edges with a heat gun to form it into a wide U shape, so that it fit around/above the PCB. I then lasered a front plate to hold the LED display, and friction-fit it into the clear top. I tried to laser holes on the side of the case for the button and USB port, but the plastic caught fire. Not good. I was able to scrub away most of the burn, and finished the holes with a Dremel.
Ta-Da! Even has a nice bow and everything. 217 Muons counted in about five minutes.
What did I learn?
• Start your projects early, especially if your project requires ordering parts from the USSR.
• Geiger Tubes can be perishable. Over time, certain fill gasses can react with the metal of the tube, or the gasses can escape entirely. This kills the tube. Be wary of New Old Stock (although there isn't much choice in the reasonable price range. Over-order!)
• If you can dream it, there's probably an online messageboard full of people who know everything about it. Be nice and they'll probably help you out.
• If you have the time, do it right. Hacking doesn't always turn out faster than doing it right.
• The Swiss are awesome.