Jim's Beer Kit

Hi All, I've been looking through the various posts on maintaining fermentation temperature, and have decided that an insulated cupboard type approach would suit me best; probably out in the shed. But there are a couple of things I'm not sure of, so any advice to a newbie would be gratefully receive...

I have a similar issue with a tesco kettle element and a stainless keg. I've seen white plastic plumbing washers used to pad out the thin wall - that seemed ideal as they're cheap and easy to get, but all the ones I can find seem a couple of mm too big to be a good fit on the tesco elements. Because...