Made my first under quilt from the Sports Authority down throws. Trimmed the perimeter of the throw with grosgrain ribbon, sewing it to the throw with two rows of stitches to create a channel. Down the length I pulled gutted paracord for the suspension. On the ends I used bungee cord with cord locks so the ends could be drawn in to shape the UQ and prevent gaps.
I made this UQ for use with my indoor Brazilian hammock. The throws are pretty heavy (25.5oz finished), don't compress too well and kind of thin for backpacking use. It's basically a 3/4 length UQ and works just fine indoors. I sleep in a top quilt with foot box, so my feet haven't been getting cold. Mission accomplished. Now to make a TQ for the throws.