I had tried to hatch some quail eggs with a very small incubator that I found on E-bay that came with 4 quail eggs. Basically the short fall was that there was a temperature drop that did in the little guys. After no success with the little yellow flying saucer I decided a try at my own small incubator.
I was at the vets and there was a sign "Free coolers" which were basically insulated shipping boxes for meds that need to be kept cold. They were heavy Styrofoam at about 1 1/2 inch thick 13x 15 x 10 inches tall. Certainly enough to handle a temp swing.
I took a small light socket and attached it to a piece of chimney flashing to help reflect the heat. I did this all with only 7 watts! Being that I wanted to monitor whats going on i cut out a hole in the top and siliconed in a piece of plexi glass. I did this by cutting a hole a 1/2 inch smaller than the plexi glass then scribed the plexi glass shape into the styrofoam and cutting a recess for it. This way it helps seal in the heat.
I then cut the side out to mount an electronic temperature and and humidity unit in the side. I took the probe and pushed the mounting tang into the side and let it run for 24 hours to check the temp at the height of the probe. After figuring the sweet spot of a 100 degrees I measured and pushed in a couple of single sided razor blades as a shelf to hold a piece of 1/4 x 1/4 mesh
If you look closely you will see two holes in the lower side by the light. these were for fresh air flow. These were made by heating a piece of 3/4 inch tube i had and plunging into the styrofoam to melt a hole. I also did this to the lid at the far end to to create an air flow by the "chimney effect"
I found that rotating eggs would prove to be a chore that ultimately lets out heat and the eggs roll around like crazy making me nuts. I took some plexi glass and cut into strips and fuses together into a rack that holds or controls the eggs. Basically all you have to do is slide the rack and all the eggs roll. I know its not pretty but it was quick and did the job.