how well would this work?

It should work just like any other incubator.
I had looked at making this when I first started incubating eggs,
but used an aquarium instead.

The still air incubator that I bought at the feed store for my last set
of eggs is basically a styrofoam shell with a heating element at the
top. Same basic design.

 

Pretty much making this now. Have most of the stuff just a few more items then hopefully start building it and testing it out how well it hold temp and humidity. A few have built this and used it on this forum....