...an outdoor enclosure that would protect against the elements so you could you house your detectors, filtration systems, etc. Could you describe what the ideal enclosure would look like...i.e. dimensions, materials, and special components needed, approximate price point, etc.?

Materials:
Something that provides shielding and doesn't breathe, or allow sunlight or rain inside. Also something that won't rust and can take a few years or more of exposure to the elements.

Dimensions:
Width: 24"
Depth: 22"
Height: 36"

Features:
Cable run for power
Raised platform inside to keep everything off the ground
Upward facing vents front and back to prevent wind from pushing rain inside
Access door on the side

Fun remaining problems:
Creating ducting from the vents to the intake and exhaust of the air purifier while still allowing access to the Geiger counter.

So I've left the setup running continuously over the weekend, and saw levels drop to 90 CPM and stay around there most of the time. There is little to no possibility of the mica window on my GC distorting the way it is positioned, which makes that first reading a bit of an anomoly. That is, until I saw it raising to 160+ again, when the heater was turned on. Will know more when I get the radon detector.