It's a bit late to engineer around the idea, but something to consider for watering your plants would be running pump(s) with lines up to where the plants are growing. You could run the pumps all day (for moss or something) or just set periods to water your plants. Something to consider... Personally, if the humidity is high enough I would do some emersed Java Fern and lots of moss on the cement; It would be a very low maintenance background that is constantly changing. Some vivarium guys blend moss, buttermilk, and some fern leaves/spores in a blender and then paint the mixture on their tanks. It is a a pretty good way to get a large area of growth.