CH, I just ran down the road to the neighbors house to take some pics. (Your welcome).... Anyway, I put a $4 computer fan in her little giant a year or two ago to help her out. I want to say it's a 44mm. It fit right inside of the elements. See pics. And also a pic of the phone charger we used. She hatches well over 80% with eggs she gets from me and a lot of times higher. You do not need a full 12v for that little styrofoam job. You just need to move air and not too much.
Here, I just went back to the neighbors and took a pic of another one that I did for her. It is similar to yours. Now, don't make this any harder than it is. This was done using 2 deck screws. You don't need spacers doing it this way. Screw the screw in until you get the desired height. She hatches a lot of birds in these incubators I set up for her.