I'm not sure if this has been said or not, but a trick i came up with to help with humidity is to take some paper towel, put in on the screen soak it to the point that it is just about to start dripping or even let it drip a bit then cover it with tinfoil and a towel. My BP is in a 40 gallon tank and by doing this and misting once a day i can keep the humidity between 50%-60% even with a heat lamp on. And if the heat lamp is off it tends to get around 70%-80%.