If you are going to go through all the effort to create a proper vacuum, and then isolate all the little penetrations needed to maintain whatever is inside, just throw the wet clothes into the vacuum and call the thing a freeze dryer. No sonic required. A heat lamp inside a vacuum chamber would probably dry stuff using much less energy than either sonic of hot air.
I'm not sure whether organic materials would be very happy with all their water content getting sublimated out of them due to the sudden drop in pressure. The result would probably look more like cotton jerky than fluffy towels. (If anyone has a Youtube link of such a reaction, though, I'd love to be proven wrong!)
