I've done a variety of backing methods, including making a too-narrow piece wider by cutting it into 2 triangles and sliding them up/down until I had the width I needed and then sewing the 2 triangles back together (using a great tip with illustrations from John Flynn). On the quilt that I'm piecing now and am almost finished, there are no straight seams. Everything is curved and putting this quilt top together was a nightmare and I'm convinced that a pieced back would cause me even more problems so I've just ordered 3 yds. of 108" wide backing from Fabric Depot. I haven't received it yet, but it looks good on my computer screen and the price is reasonable.