I started out with a fridge incubator, as my "big" incubator. It was really tacky, and even though it worked, it smelled bad, there were styro foam particles every where, and I was getting tired of it.
So, I had just met this man that lives a few blocks away from me, and the first time I met him, he showed me around his place, and even gave me this big ply-wood shipping crate. It was Insulated with 1 1/2 inch polysterine. I had just gathered up enough money, so I went to a few stores, until I got everything I needed.
In the pictures you can see that I covered the walls with strand board, and painted and sealed it. I sealed the walls, and the back side of the door 4 times.
Here are the pictures.
Here you can tell that it was a shipping crate.
In this picture you can see the weather stripping foam tape that I used to insulate the door when it is closed.
It has 2 small desk fans, 2 75 watt light bulbs (bulbs aren't shown in the pictures), and is controlled by a wafer thermostat.
You can see the wafer thermostat placement relative to the light bulbs, (Note: These light bulbs aren't what I use to heat this incubator.)
You might also be wondering why the adjustment screw, and the whole wafer thermostat assembly is inside the incubator.
It is because the walls were to thick to place it on the side of the incubator.
2 hatching trays.
Here it is with 83 eggs in it.
The temperature holds perfect in this incubator.