I'm using a space heater in the room, set on low and 80*, to bring temps up from the regular house temps and I put jars with paper towel wicks(Think molotov cocktail except with water) in front of it. I also leave my water container to water plants full, plus I add a bit of water to the drip pans under the pots(not enough for the soil to soak up) and I hang wet cloths in the closet.
I go through about a half gallon of water a day in evaporation. But keep in mind, they are not in a small or sealed room. I have to raise the humidity in the whole bedroom.
Someday I'll probably end up in a tent that I can control easier but for now I'm still working with what I have.