jackrae:
I Of course that covers the worst-case temperature scenario so you will also need some form of thermal (proportional) control to to reduce the heating and so maintain a steady temperature within the enclosure if the external temperature is higher than the lowest expected external temperature.
Thanks for this, puts things in a different light and I will test this too. I have found examples (and data) from payloads using a power resistor and a load controller, I'm guessing this is the bit of electronics that keeps an even temp rather than switch the heat source on and off when a trigger temp is reached i.e. less of a peak and trough profile with the load controller? I have seen one example of 8 degrees being maintained inside the box for 3 hours in a freezer at -18 (2w resistor). I'd be happy with 2 degrees for 2 hours.
Best wishes
Phil