For "holding in place while you steam," small plastic spring-loaded clips are handy. Not strong enough to leave a dent in the cloth, just enough to stabilize while you steam. Riverkilt speaks of hanging kilts with pleats clipped and a small fishing weight to keep them straight.

As for how many lines of basting -- how big is your pressing surface? The weight of the kilt hanging off either side of pressing surface can pull pleats out of alignment as you try to press them. The more basting, the less fiddling and mis-pressing. It is time spent doing one or the other.