Computers aren't really designed to work in that kind of an environment. The only thing you could really do is completely seal off the case from the environment in that room, but then you run into ventilation problems for the computer, leading to heat build-up. Years ago I built a system used outdoors at a dock on the sea, constant exposure to moist salty sea air. I managed to find a heavy-duty steel case electroplated with zinc designed for such an environment (don't remember who made it). I don't know how resistant zinc is to whatever you've got going there, but something similar might help protect the insides better. There's still the issue of ventilation. If you seal it off, you're going to get heat problems. Might be able to dissipate that with liquid cooling, but it might not be enough.
One of the newer plexiglass cases might also even be more resistant to corrosion. If sealed off and with a closed cooling system, like liquid cooling, it might make the computer last longer.
You could also move the computers to an environmentally controlled room, but you probably would have done that already if the computers didn't need to be where they are.
