Last night dipped into the mid 40's and the underquilt performed quite well - I was toasty. It's just long enough and wide enough for me and my WBBB. I'm using the simple JRB type suspension for now. I have enough down left over so I will be making 2 draft tubes for the ends.
One thing I would have changed - I should not have used grossgrain on the edges. I should have used the ripstop and made channels. The grossgrain does not scrunch well - I noticed small gaps on both ends. The baffles will solve that problem. The grossgrain - all 7 yards of it - isn't really needed.
Overall, I'm happy with the results. It's a bit heavy, but not bad at all. I learned a great deal on this project, so the next one will be better. I'm sold on down now - it's definitely the way to go for light, warm insulation.
I got in a fight one time with a really big guy, and he said, "I'm going to mop the floor with your face." I said, "You'll be sorry." He said, "Oh, yeah? Why?" I said, "Well, you won't be able to get into the corners very well."