Lmp, since your incubator is not full, you may wasn't to try putting a couple soda bottles full of 99 or so degree water in there to help stabilize the temperature. The mass will help reduce the temperature swings when you open it to turn the eggs as well as hold a little heat if there is a short power outrage.
Fill the bottles with water very close to the incubator temperature so you don't overheat it or shock it with cold temperature and make it overwork. Too hot is worse than too cool.
If I'm wrong, I'm sure someone will correct me.