I have made three, and used flannel as backing. The first one has no batting. It is warm, but you can feel the seams. The other two have a thin batting, and all are tied.
The nice part of making denim quilts, is the fabric is free. I did find a little problem. A lot of the jeans have stretch in them. I was selective, and didn't use them. I am saving jeans for my next project.