I have had four suspension forks which I store in my unheated garage. The temperatures here are similar to southern Manitoba, so it will get down to -30C inside the garage a few times a year but it is mostly between -10C and -20C.

I have had two Marzocchi 320LCR forks. One suffered a failure of the air spring on a very cold day. The other is still in working order, although it is not currently installed on a bike. The remaining one is about five years old.

I have an Ohlins coil spring fork which is four years old and which is ridden mostly off road and fairly hard. It is just fine.

I have a Wren inverted fork on my fat tire bike. It has dual air chamber springs. It has two winters on it and it is just fine.

I might point out that automobile suspension dampers are often stored outside at -40C and operated at that temperature with no adverse consequences.