I am not familiar with that incubator. Can you install a small fan to circulate air? If you are getting uneven temps, the air may not be getting enough circulation.
You might be better off building a small incubator out of an old cooler (ice chest type). There are a lot of good threads and illustrations on how to do that with some heat tape, fan and some bottles of water. Same theory as the large freezer, but on a smaller scale.