How can i create a incubator without buying anything?

I have some fertalized eggs arriving, and ive heard if you put a tub of water into a box with a bulb in you can hatch eggs, I desperatley need one, i have quite a big plastic box, a small lamp with a bulb at 100w. But should i tape tinfoil around the box so it does not heat up to much or could this kill the eggs?