Hi Rick, I use the bought items from Seuthe (wonder if it is known in the UK). There are various types which run with either 6 or 12 Volts. The advantage is, that they use a ceramic resistor which produces heat. The ceramic is shaped with a small tunnel, though the capillaries-effect "soaks" up the liquid, which will be overheated and produces the smoke.
I have made some tries with selfmade items, but hasn`t been very successfull as they also produce a greasy fog which will fall down on superstructure and deck and soil it.
Jörg