Since the rubber coating comes out of the can initially in a liquid form, it will require what we like to call a bridge. As you can see we created this "bridge", by using something as simple as scotch tape. Please use just enough to cover the hole. You do not need to use as much as we did in this image. Now you can spray away!

We highly suggest spraying the entire housing to cover any discrepancies in the metal like the seams, etc and other knock outs that may not be completely closed. You may do the same for other housings (not just step light housing) that may have knockouts.