double boiler or bain marie two messages together
Use oil like pint O shine does
Here is his link http://www.youtube.com/profile?user=pintoshine
I am a Master Steamfitter. I operate and repair boiler systems. Water has lots of problems it will eat holes in your kettle in no time if water treatment in not used. And you can’t leave it alone for a second if something goes wrong the steam will explode (not a good thing)
The heaters you get at Wal-Mart has an element in the oil and the oil transfers the heat. This system sounds like what you are looking for. .