Mainly get moisture when warm air hits cold parts, in this case its cold air hitting hot parts. I duct a 5000 btu window unit right into my cards and have no problem "other than my electric bill".
What's a 5000 btu window?
However I believe that cooling air with an evaporative air cooler is much more energy efficient.
Or a combination if you care for comfort.
I'm not sure about the energy efficient aspect at all - I did consider an air conditioner. My rigs will be pulling around 4.8kwh total. A conditioner would add 3.5kw per hour!
EDIT: Maybe after reading there again I've misinterpreted you. I assumed an evaporative air cooler was the same as a conditioner - never heard of them b4.
What about just venting the heat straight outside? Then at least you're not trying to cool the heat that's being produced. I guess air is going to be coming into the house from somewhere with that kind of venting?
If you had all 4 rigs next to a window that had a few beefy exhaust fans I assume that would at least get rid of the heat. Unsure how that would effect the rest of the basement though.
i think that's how it works. get fresh air from outside and blow the hot air outside again. vent holes needed, though.
paint skills! of course the left and right part need to be connected to the outside.
Or run another 6. 