As an update, this week my outdoor cameras withstood -44F with no enclosures or other protection from the cold, and there was no degradation in picture quality.
I can't say that all cameras will perform like this at low temperature extremes, but it is sure worth trying before spending money and time on heated enclosures which can be expected to fog over and prevent you from getting acceptable pictures from the cameras.
Powering my Cameras and Cold Temp ?'s
I'm using 5 X10 Nightwatch2 b/w cams outdoors here in Ottawa Ont. and I've not had a problem with them down to -25f without heat or protection. They are powered over a 60' cable which uses rj45's. I've extended a couple of cables (better quality phone extension cable) by 20' or so without signal degradation. Newer digital cameras really shouldn't need a whole heck of a lot of pampering.