AnimalControl - great job.
Glad you like the draft stoppers. I copied them just like Ray Jardine did. The name of the inventor of draft stoppers is probably lost in antiquity. I have known of draft stoppers for decades and have never known anybody that could name names.
As for an underquilt. When I started mine I wasn't too sure about a karo step under quilt, but wasn't concerned since I had already finished our under quilts. When I was finished I was starting to change my mind. After having the karo step quilts hanging in the basement from one end for many months, I am of the opinion that a karo step would work fine for an under quilt so long as the karo steps were not too sparse and the quilt was over stuffed. I over stuffed ours 20%. They have been hanging vertical in the basement since spring and there is no shifting of the down whatsoever. I notice that most or all people tend to over stuff their quilts anyway (even JRB advertise theirs as overstuffed), so overstuffing a Karo step would be normal practice.