I think that I always assumed that the nakedness was Symbolic at the same time as I always found it a bit silly, because Symbolism was clearly the only excuse. For one thing, I reckoned they would be cold. And for another, they were running about naked. I can see the practicality argument, but if they really want to get out of the Barrow-Wights clothes then Bill could call the ponies early and they all stick on a spare shirt ;-)

I'll have to have a look at the read-through. On first glance, it looks fascinating.