I'm retired and have no duties that require starting my tractor in such cold weather.   Besides - when it's that cold - I don't want to be out in the cold either.
However - contrary to my better judgement - I've started my 
M6040 a couple times with temps down as low as  -20F.   I ALWAYS have a battery tender hooked up in the winter.   Nothing else.
The tractor will fire right up.   It coughs, grunts, blows smoke for a few seconds - then smooths out and runs fine.   I use PS white jug in my diesel fuel - year round.
If I had animals that required daily maintenance -
- battery tender
- lower radiator hose tank heater
- cabbed tractor
This would be a more economical alternative to a heated building/barn.
JMHO ......