Update: tried a pre-loved WNNN last night, under a Nature Babies wrap and it was no better or worse than the usual set-up, although a bit slimmer and very good looking! So he was damp around the legs when he got up at 7ish. Might have to try it with wool or fleece once it's been washed and dried. He's so wriggly, I wonder if the disana wrap might be the way forward.
Next up: A Mama Knows. Bought four, and still waiting for two of them them to dry after a pre-wash. We'll see.