You would be giving up the tensile strength of the glass on the inside. If, for instance, a wave dropped you on a rock you would wind up with splinters in your butt. One way to overcome this weakness is to add ribs to the design (which doesn't work really well for kayaks). Examples of this are Adirondak Guide Boats and traditional canoes of canvas over cedar plank construction. The ribs provide strength oriented 90 degrees to the planking.