I would still invest in a second thermostat. I have two thermostats on all my racks and my incubator. You don't want to risk a thermostat failure and loose everything in the incubator. Albert Clark's advice to get a hygrometer certainly will let you keep an eye on the humidity in the tubs. With tubs that are sealed, I have usually just check them weekly and added a little water in the corners as needed (I use the medium less method by the way, so the water is not in direct contact with the eggs). Like Deborah said, I would not open your incubator often because it is small and will loose heat rapidly. Do you have any water bottles in it to help stabilize temperatures?