This same question was asked a few weeks ago
Obviously moisture is a big problem, why not try water cooling or something out there like Dry ice.
Also i watched a video on Vegetable oil cooling. All you have to do is take all the fans of the computer (including the psu fan and gfx card) and then submerse the motherboard (with the other parts plugged in) in a tank or some kind of holder for the vegetable oil.
Also you have to keep the floopy/cd/dvd drives and hard drive out of the oil. But everything else can go in.
Edit: It's also recommend that you get a pump or filter thingy that would be capable of pumping oil around, so that's a no go on the fish tank pump