I still wouldn't use it for backing. Remember all elastic breaks down over time, faster if exposed to heat (like drying in a clothes dryer). Think of the elastic waistbands in old underwear, old rubber bands, and the like. Limited life expectancy, unlike pure cotton. Do you want to do all that work using something with a limited life expectancy? I wouldn't. Just mho. I know that's not what you want to hear, sorry.