That is a creative idea. You might get a lot of condensation dripping off your ceiling, though, and on your plants' leaves in the morning. I had a 225 gallon fish tank with an open top and a waterfall filter in my 14x48 high tunnel. The humidity can be nice when the outside air is dry, but all my plants were wet with condensation every morning, and a lot of my tomatoes got early blight. Wet leaves promote disease.