Prototype Build Notes, July 2019 Update:
Instead of attaching the two 6ft steel piano hinges to the front/top surfaces of the 2x4s (which creates a gap when the hinge is closed at 0 degrees), one flap of each hinge should be sandwiched between the 2x4 and the MDF at the top back and front bottom pivot points. This would require one to purchase a chisel and carve out recesses (a router is superior for this task, but $100+), in the two 2x4s, for the hinge flaps and hinge pivot point clearance.
When the MDF sheet doors are fully closed, the hinges will be at a 90 degree angle, and when fully open, 180 degrees. When in the closed (90 degree) position, the exposed face of each hinge flap should be flush with the surrounding 2x4.
This allows the MDF doors (with sheet metal covered plane/edges) outer edges to mate with with the 2x4 surfaces (also with sheet metal covered faces) in the two side panels. These closely mated flat surfaces enable the use of electromagnetic compressible gaskets, which create a strong shielding connection between the two conductive pieces/layers, by filling tiny gaps in the Faraday enclosure's conductive skin layer.
Once the MDF doors are closing flush, their unhinged edges now touching each other, a latching mechanism needs to be devised to keep the doors pressed into each other, again to create a strong electromagnetic seal. I recommend something like this latch product. With the MDF doors closed, imagine there's a 2x4 or 2x2 board pressed into the internal corner that's created by the meeting front lip of the MDF doors. That board attached to the front lip of the MDF door would have affixed latches that grab the opposing door from the inside, to compress the electromagnetic gaskets placed along the board/front lip of the MDF doors.
Note: 2x plywood or hardboard sheets can be substituted for the 2x MDF sheets being used for hinged doors, and could provide longer lasting service, given the repeated hinge opening stress. Be certain to use new plywood/hardboard with an exceptionally flat plane/no warping, for adequate conductive skin layer contact at all contact points.
Anyone that wants to work with my SketchUp files: they are from the SketchUp 2016/2017 version, and should easily import into the SketchUp 2019 trial version.
High Redundancy Ventilation System, May 2022 Update:
These products provide simplified setup and better redundancy over the previous configuration. The below suggestions provide FOUR independent fan power channels, meaning all four power adapters and all four fans would have to fail simultaneously, for air to stop flowing.
Then all four blackout buzzers would have to fail.
Then the CO2 monitor inside the enclosure would also have to fail.
Even if you somehow sleep through all four of the blackout sirens, three of the fans should keep running on their 12v DC battery backups until you wake up (the fourth fan runs directly from a power adapter, in case all three 12v battery backup units fail simultaneously from the same potential/unknown design flaw). Also if you have the money, and you don't want momentary blackouts at 1am waking you up, I recommend an 120v AC UPS battery backup unit ($170) to plug the surge suppressor into.
If all nine of these independent devices or independent fan power channels fail at the same time, and the occupant fails to wake up, only then is there a chance of permanent brain injury or death. Consider also a sleep monitoring oximeter with alert function, as yet another additional backup to wake you up in the event of a catastrophic system failure.
Do not gamble your life on dirt cheap bargain basement products -- everything listed here has been specifically selected for long term reliability, safety, and affordability: around $750 for everything below.
How to use these products together
Every product above is numbered, and referenced with brackets below.
Exchanging the air in a sealed/solid Faraday sleeping enclosure:
Measure the dimensions of an all aluminum or all copper radiator, and cut four appropriately smaller sized holes into the sleeping enclosure (through conductive skin layer, and MDF wood layer underneath). I recommend putting the intake holes at sleeping head height, at one end, and exhaust holes near the floor, at the other end.
With two holes cut into each enclosure end, cut and apply the RF foam gasket[2] around the openings. Then remove as much paint as possible from one side of an aluminum radiator[3] (sandpaper/acetone/dremel), and mount the radiator to the enclosure, squashing the unpainted side into the foam gasket[2] surrounding the hole. The enclosure's conductive skin should be contacting the RF foam gasket, which in turn is contacting the aluminum radiator.
We're using them as cheap RF waveguide air vents:
https://marshield.com/rf-waveguide-air-vents/
For the optional LED voltage meters, wire strip[7] voltage meter[13] wires, and crimp the red/white wires together into a fan connector[14] 12v power pin, and crimp the black wire to ground in the fan connector. Plug the fan connector[14] with crimped wires inserted into the connector, into an empty header on the fan monitoring board[5]. These voltage displays are to glance at before bed, to validate that each fan is getting 12v power. Using a voltage range alarm would be better, but those are not available as off-the-shelf/plug-and-play solutions.
Place and turn on the CO2 detector/monitor[1] inside the enclosure (and wear a sleep oximeter alarm if you can afford one) before you enter, seal the enclosure doors shut, and fall asleep.