http://www.nisbets.co.uk/products/produ ... Code=CE706
Not to use as a boiler, but because of the way they are heated. These use either a 3kW or a 6kW electric element, but it is NOT an immersion element. Instead it is in a separate compartment bolted underneath the boiler. It is in contact with the boiler skin, and also protected with boil dry cut outs etc.
Now if it is good enough for a water boiler why not for a still. Has anyone tried fitting one of these elements to a keg? Just put it in physical contact with the base of the keg, no welding or drilling reqd. Spare elements are readily available.

With decent insulation it would probably heat up nearly as fast as the same size element inside the keg - but possibly with less chance of burning. Has anyone tried?