i did a king size quilt on my flynn, actually it was the first quilt i ever did on the flynn.
the best way to deal with rolling up something this size on a flynn is with 2 people, one at the top holding the rod level and straight and the other doing the actual rolling.
you need to mark registration lines every 6-8 inches down the sides of the quilt. this will let you know that you're rolling the piece evenly the entire way.
i also do all of this quilt rolling on my bedroom floor because the carpeting provides a little bit of drag which actually assists in the rolling on of the quilt/batting/backing.