I had thought to finish this with Kona Ash, but opted instead to use the backing and batting originally intended for the Double Hourglass quilt. After looking at the pictures of the DH I saw how badly I had laid out the blocks. I did not realize that they had a specific orientation and the random way I had sewn them together just looked awful.
I had already pinned it and gotten it ready for quilting, but I unpinned it and discovered that the backing and batting were an appropriate size for the Rail Fence top.
The now discarded Double Hourglass top is rolled up and stowed in my scrap bag. Perhaps one day I will have the energy and motivation to unpick the seams and redo it.
The Rail Fence is backed and bound with white and looks great. It finished up at 32x36 inches before washing.