My husband made me an incubator out of a thick Styrofoam cooler. He did it using a 60w bulb that says it only puts out 42w and hooked it to a dimmer so I could adjust the amount of heat it puts out. We also installed a computer fan and I have 4 holes in the Styrofoam. One hole behind the fan, one on top, one in the side, and one on the front. I am having trouble holding the temp study. I have adjusted the dimmer several times and the temp keeps going up or down. Would more holes help it hold study or what can I do to hold the temp?