I had the same problem with humidity. Here's what worked for me: go to Home Depot and buy a sheet of plexiglass, and a plexiglass "cutter." It should cost you about $30. Measure out the length and width of your screen top and cut the plexiglass to size. Drill a couple holes on the cool side for ventilation. Replace screen with plexiglass. Boom. Humidity has been holding up great for me.
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