The most morphable long skirt I've found is DAZ's morphing fantasy dresses. They've got versions for V3, SP, and Laura. There are all kinds of morphs built into them. Morphs for sitting, kneeling, walking, climbing. Morphs to swing different parts of the skirt in various directions, shorten it, lengthen it so it trails on the floor. And morphs to shape the skirt so it can go from sleek and silky to full and stiff. If you want a really full skirt, get the expansion pack. It has an overskirt that has even more "full" morphs. If you use them all, you can have a skirt that puts Scarlett O'Hara to shame.