I'll explain this as best as I can. My husband actually did most of the work, but it only took about 5-10 minutes.
Inside of lid: we chose an empty space in the middle to put the fan. We poked 4 holes (1 at each corner of the fan) to attach it using zip ties. There is a vent hole directly above the fan. We ran the wires for the fan through that.
Here, you can see the short pieces of a straw that we used for spacing so that the fan wasn't directly against the lid. That gap allows for better air flow.
Here's a view from the outside. We used some plastic pieces to keep the zip ties from pulling through.
I don't know much about the wiring aspect. Basically, the wires from the fan got connected to the corresponding wires on the wall charger. Then it was all wrapped in electrical tape... Though we'll replace that with the heat shrink stuff before next time.
The fan blows air up and out the vent hole. I'm not sure if that was the best way to do it, but its working fine. I end up covering about half of that hole during hatching to keep the humidity up. With the fan and the other vent holes, there doesn't seem to be any issues from lack of air or anything like that.
Feel free to ask questions. If I don't know the answer, I'll ask my husband later.
The air gets sucked away from the eggs? I thought the fan was to blow air onto the eggs?