I misunderstood one of topshelf's questions. We route around the outside of the housing, and clean up the rest with a chisel. Even if the depth is only 1/2" (like in the knee brace housing shown in the photo). If you try to do the center, the router will 'fall into the hole', since it's riding on the template base which has a hole in the middle. The exception is the knee brace housing, which is only 2" wide, so the router easily reaches the center.

Also note the "full metal jacket" of safety gear used in the video (ear, eye, lung protection).