I would consider liquid cooling.

Not immersion, but heat-sinks screwed to aluminum plates to which there is aluminum tubing brazed on the opposite side.

The cooling medium should be distilled water.

With pumps moving water through the tubing attached to the heat-sinks you can use a small fan-cooled radiator adjacent to the PC. Or, provide a small refrigeration unit and a thermostatically-controlled re-circulation valve to control the temperature at the heat-sinks.

This is how electronic equipment is cooled on navy ships, etc. where computers, radar, etc must be kept clean and dry in an equipment enclosure onboard ship.

This would have the benefit of avoiding dust-laden air being blown across your computer's electronics.