The larger the quilt, the bigger the chance of getting wrinkles in the batting.
Try heavily starching the backing.
Lay out the backing and pin or tape it so it is taut, but not stretched... then add your batting and top.
Baste well... On large quilts baste even more than what you think you should :wink:
Start in the center of your quilt when quilting, and work out to the sides and top. This helps "push" the fabric out to the sides :D:D:D