I have made several hundred Linus quilts with flannel backs in the last couple of years. I always prewash all fabric for those quilts. I pin bast about every 4 inches and don't have a bit of trouble. I use a walking foot and a decorative stitch. I only quilt about every 5 inches or so. At the most I might have one or two puckers. I have a Bernina 1260 but I have also done them on my newer Bernina. No problem.