I only mount the backing.Then float the top.I make sure I have extra backing.To float the top,baste the batt on to the backing.Use channel locks to get a very straight line.Then lay the top along the straight line and baste down.I usually have to pin every few inches to get it straight.Take a large square and make sure the corners are square,pin a little and baste down.I have a pink centering tape that keeps the sides square and baste them down as I advance the quilt.My quilts are always square when I take them off the frame.And also it is veasy peesy for my customers to apply binding when the quilt is basted all the way around.