Most notable damages that occur at those temps are with the lenses. The cold temps shrink the casings and bend the metal causing them to be out of spec at normal temps. Not always but it happens. Other issues are with cracked LCD screens. However if the camera is in use the entire time it can generate enough internal heat to keep it at or above 0C.
Just note that it's extremely dangerous to Canon equipment to expose to temps below 0C. It also voids the warranty.
Sometimes though it's worth the risk for shots like this, especially if you have an old rebel that you can afford to replace.
Kernuak said:
Thanks all. Settings were 24mm f/1.4, ISO 1600, 4 secs, in continuous. Some had Rebel-type cameras which coped without problems, despite -28.5 C. I think the shooting star type trails are probably satellites.