I would think doing it that way might be difficult to have the upper edge be neat. I would make it like an apron or skirt waistband so the piece you're attaching the Velcro to is smooth. I would also make the under curtain less than double. If you want the valance, it can be double. Plus, I'd use two pieces on the curtain for accessibility - three if you're turning the corner. it does sound like a good idea.