Presumably, you won't be at -40 degrees Celsius all the time. If you use a regulator to dissipate enough power to raise your temperature by, say, 45 degrees C, to put you comfortably inSIDE commercial temperature range, you may not like what it does when ambient temperature is in the commercial temperature range.

You will need some sort of temperature monitoring and dissipate power into a resistor or light bulb, in order to get the temperature into the range you desire, with a control of some sort of your choosing that turns off the power to the heater when it isn't needed.

RE