Assuming that you will want to wash it every now and again, do you really want or need to sew rubberized backing to it? If the current method of layering it over an old rug is working, don't mess with it. I think it's a great idea. And most people in our area take their shoes off on entering a home, so if that's a habit you follow, I don't think the rug/quilt will suffer too much.