I have a 2-person outdoor swing with a canvas seat and back. The canvas (not the decorative cushion) is torn across the width of the seat about 3 feet wide and about 5 inches away from the frame. I sewed about 4 inches of it then tried adhesive backed vinyl patches over the entire area but as soon as I sat on it, it split open again. Do you think iron-on patches will work if I iron them on from the top and from the bottom across the entire tear? Or does someone have a better, more durable idea? Thanks!