With the A/C on, humidity should be reduced. As long as you don't leave a refrigerator door open for hours, I don't think it will be an issue. You could also cut a piece of matting that would fit in the pan and stop 'wave' action. Periodically remove it and clean it off with bleach water.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI