ok, typing one handed tonight
Aris: it's a brinkman upright water smoker, but I checked it out tonight in a B&Q kettle barbeque and it works just the same.
eddy current: good point, I wasn't aware of that, the one I've got has all the heat in the barrel and the point is a solid slug of metal sticking out of the end, most of the heat is in the barrel.
Vinner: chips were over 90% humidity when I drilled them out, my initial test just produced steam even though I felled the tree 3 years ago. A good drying helped enormously. The depth of chips doesn't seem to matter if they are loose, smoke still gets through. I checked it every hour or so through the day and gave it a wiggle or a top up. it worked best for me without a lid.
off to bed now so Mrs D can check the damage on my hand...