Shawn
I have a recommendation that might help.
I made my own incubator as well using plans found on the forum plus some inovation of my own and I am currently in day 15 incubating 19 eggs from my 4 hens. Temp inside rolls from 97 on the low end to 102 on the high. All my eggs are fine - its the average temp you are looking to maintain. My setup has fans for a forced air setup vice the still air models some have built. I also have built an external handled egg turning setup so that I do not have to keep opening the incubator for this task. Plus the eggs are up top of the box so they stay in the heat longer during the cycling of the thermostat rather than being in the bottom of my converted igloo cooler.
The recommendation I would add would be for heat stability and retention during the on and off cycle of the thermostat is to add smaller rocks that heat up, and then retain the heat longer like heat sinks (the idea came from an episode of Survivorman on Discovery channel).
Since adding the rocks, the air temp stays about a constant and the on and off of the light and the homemade thermostat has not been an issue in keeping th eggs at a near perfect temperature. So far 19 or 19 candled with great development and embryo movement as of last night (I was hoping just to get 50% of them to this point by now...I am keeping my fingers crossed that all 19 will keep going strong the last week of development).
I will try and post some pics on my setup in another post, but try the rocks for heat sinks - they do not have to be very large - just add them to where you have space in your incubator/cooler to hold heat. It helped me.
Best of luck.
Brian....
