Did you not have any issue with them getting wet? I thought if you run them in extremely cold conditions the heat would cause condensation and then you would start getting water all over your miners which everntually would cause big problems. At -20 i thought maybe your fans could seize up as well unless you were running them without them due to it being cold enough already?
Backwards.
Warm humid air flowing over COLD item causes condensation.
The issue with electronics at extreme cold is that it can stop working, or just not work right - but if it's running before the outside temp gets that low, the internal heat generation can often keep an electronic device warm enough to KEEP working correctly.
One possible trick to use, if the shed is close enough to the house ANd if it gets warm enough - run a duct from the hot part of the shed to the house heating ductwork, with a temp-controlled fan blowing the air from the shed to the house and a flapper valve set up to not let the air flow back the OTHER way.