I use a heat bath for tempering. The only problem I had was a small fire when I spilled some oil on the flame because my very sloppy manipulation of the container when stirring the oil to make temp even. i was doing it outside, i was wearing gloves and I was doing it on a very non-flammable spot 
I do it that way because I can control the temperature very precisely with my kitchen thermometer. I use sunflower oil because is cheap here. Soybean oil is cheaper but if it smokes, it stinks. I temper at 200C or less than that which is ok for the oil I have. I finish my french fries at about the same temp.
For cooking at low temperature I use a box with very thick styrofoam walls I scavenged from a molecular biology lab. i heat up cheap vacuum sealed beef to 65C in a pot with water and then transfer bag and water to the box.
It keeps temperature very well and I control it by checking every hour and reheating a cup of water taken from the box into the microwave and putting it back in.
Maybe I will try the trick with hot oil for tempering. Styrofoam melts at 240C so it is doable. I will try to find a suitable box. Long but with low volume, to use as little oil as possible. I will put the contraption in a big pot to contain the spill if it happens. This way I don't need a thing with a thermostat.
I do it that way because I can control the temperature very precisely with my kitchen thermometer. I use sunflower oil because is cheap here. Soybean oil is cheaper but if it smokes, it stinks. I temper at 200C or less than that which is ok for the oil I have. I finish my french fries at about the same temp.For cooking at low temperature I use a box with very thick styrofoam walls I scavenged from a molecular biology lab. i heat up cheap vacuum sealed beef to 65C in a pot with water and then transfer bag and water to the box.
It keeps temperature very well and I control it by checking every hour and reheating a cup of water taken from the box into the microwave and putting it back in.
Maybe I will try the trick with hot oil for tempering. Styrofoam melts at 240C so it is doable. I will try to find a suitable box. Long but with low volume, to use as little oil as possible. I will put the contraption in a big pot to contain the spill if it happens. This way I don't need a thing with a thermostat.
