Green Anacondas can be great snakes. Obviously you know you will have to house them in much larger cages eventually. One good way to increase humidity is to limit the amount of ventilation which is the main cause of heat and humidity problems. If you are using a screen top on your 30 gallon you will need to cover it up as much as posible. I have had great success housing snakes with high humidity requirements by placing a large bowl of water over the heatpad. As the water evaorates from the heat it increases humidity a lot.