Don't be obsessed about the humidity, just keep water in the center trough for days 1-17 and then have both troughs full for days 18+, just like the instructions say. Your house will be fairly dry with all that ventilation and cool air, so you will need to add water to the incubator every two, or three days. Don't worry about it, just keep an eye on it and add a cup or so when the trough runs dry.
Have fun!
Have fun!