cold weather is no problem, but when it gets moisty in a cold barn, then you're fucked.
there should be enough warmth in there to keep condens and stuff outside, you don't want to have (how do you call it, daw? ) water drops on your amps/speakers/everything.

I've also got all our stuff stacked in a barn we rehearse in, amps and PA, mixer everything, but that barn is pretty well isolated.. we do throw blankets on the amps.

I think electronics can stand the cold verry well but you don't want to expose your guitar or bass to cold/hot weather changes, it's really bad for the neck etc.