So after a year of debating, I took the plunge and just finished my first down underquilt. Thanks to MAD777 for posting how he did it and for all his hard work figuring out how to cut it.
I made mine out of 800 fill down, eight chambers with one oz. per chamber. When I first got the down I thought it would not be enough but I ended up with about four inches of loft, way more than I would need for a summer quilt but it should be good into the fall. Ill try to post some shots, still working onthe suspension system, I think I will try a method of attaching it to the tie-out points of my HH clone, as a way of spreading it out. Its 42" x 52". the dark lines between the baffles is silicone seam sealer, I was afraid of down leaking out.