The main issue would condensation, if any depending on humidity.
The heat and cooling and be solved with a custom water cooling loop.
heatsink
Radiator
Pump
hose
reservoir
hose fittings
anti-freeze (stuff you put in your car)
The case can be mostly sealed at that point. You can run the hoses anywhere you want even outside at that point. Simple case air filters should keep out any sawdust, although if you want to buy a heppa (quality) filter there no reason you can't.
Unless the PC itself will be subject to rain,snow, or etc there shouldn't be much of a problem.
After that building a small cabinet to surround the PC to keep the elements out.
You can get some vent hosing and attach it to the power supply and let the hose hang down so the water can't go up the hose.