Okay, I lied...I don't use misting systems. I use dirt. Dirt is a great substrate that is awesome at retaining moisture. The average humidity of my house is extremely low, especially in the winter with the heater going, so I find myself dumping water into the soil almost everyday, sometimes as much as a gallon per day for my big russian enclosure. All of my enclosures are covered and have low amounts of ventilation, and it's still an uphill battle keeping the humidity high enough even for the species I keep (most of which are not tropical species).
I've found that misting is usually very helpful for species that will aquire water from droplets and dew forming on surfaces, but for species that need high (or even just moderate) humidity, you need to think about the bottom of the enclosure and the top. The substrate needs to hold moisture, and the top shouldn't let too much out. Full screen tops will be your enemy when you're trying to keep the overall humidity higher, as will high wattage heat lamps (which is why I usually try to use lower wattage heat lamps placed closer when possible).
What species are you trying to house?