Double-wall boiler safety/operation

[MtRainier]

I have a double wall boiler with an agitator incoming where there will be two heating elements in the jacket volume to heat the water. I'm planning to use it as a stripping still for grain-in washes.

I plan to operate it like a bain marie cooker with a little bit of water on the bottom third or so but with mostly steam in the jacket to carry the heat into the interior kettle volume. It has a 5psi pressure relief valve built in to the jacket volume.

I plan to take it safe and watch like a hawk as I'm running it, but I'm wondering if anyone here has run one like this and can offer advice on the correct way to control the heat. It will have variable solid state relays on each of the two heating elements, so I can vary the power to each element, but my wash volume will be one step removed from the heat being applied.

I can put a pressurestat on the jacket and control the temperature of the jacket based on pressure in the steam volume on top of the water, which would keep it under control from a safety perspective and would force the jacket to be a constant temperature, but that doesn't really control the heat going in to the wash in the same way that regulating the power on an element would do.

Is there a good reference on how to operate an electric bain marie boiler?

Thanks.