I worked with a Project Linus group that requested this type of finishing so have done many. Someone mentioned making the back a bit smaller than the top which is a good thing to do. I would not suggest a poly batt. It will allow the pieces to shift if you are machine quilting and you will get puckering of the back. If you are tying the quilt then the batt won't matter quite so much. There can never be enough basting on this type of quilt and if machine quilting you will need to keep a lot of tension all around the working area. If it's the look of a binding that you don't want the I would suggest a facing rather than a binding. That way it won't show.