I had planned to use a drain pipe. But a little reading led me to the inconvient truth about PVC. It starts to melt if you run steam through it, and it collapses under its own weight. So this is Aluminium Air Conditioning ducting. It arrives compressed concertina like and you simply stretch it.
Without a little insulation, it would not keep the wood hot, so some cheap attic insulation and a bit of cord and we are set. I just used a steam wallpaper stripper as a steam source and left if cook while I got on with some other bits and pieces.
Here you see the two chines clamped roughly in place. There's still work to do, but progress is progress.
Oh, yes, heavy gardenning gloves are your friend here, the Aluminium is hot, the steam is hot and the oak is hot.