I'd like to improve my glass tank setup a bit--I'm looking at switching from a UTH/lamp combo (with thermostat and dimmer) to two UTHs (and two thermostats) because my humidity is just a little lower than I'd like in between misting. I've heard covering the screen lid can do the trick, but how much ventilation do I need to offer? Are we talking a few holes or a pretty good amount?

Thanks