The primary issue will be the bulk at either end of the take-up bar is going to increase twice as fast as that in the center. You'll end up with uneven pull as the quilt rolls on the take-up bar - increasing sag in the center as you go. The take-up will start pulling the edges faster then the center, creating a "smile" in the way the quilt is pulled (edges faster - larger diameter; center slower - smaller diameter). The side clamps can only do so much and don't help much with top-to-bottom tension.