Aaah! grass hopper!! Constant temperature source is a very difficult ask. I feel sure that you will have to keep your eye on the ball even with a single ring electric cooker, because the hysteresis of the thermostat type used in those cookers has a rather wide on off spread. A way to smooth the temperature swings is to use a metal container with a layer of sand between the heat source and the bluing salt container, start with about an inch of sand.

The only lessons in my life I truly did learn from where the ones I paid for!