If you wear a down coat around camp, for glassing or other activities, it will be too damp to wear all night to sleep in. This could dampen the down in your bag, a major issue and is NOT a weight-efficient means of sleeping warm in cold conditions.
You NEED to get a sleeping bag that works at the lowest temps. that you will encounter and two down bags rated from 25* to perhaps -10*F, will cover most situations. To carry the extra weight of a coat for additional warmth and also use this for daytime wear is not efficient and can cause problems you do not want.
The mountains of BC, AK and other truly wild areas are unforgiving and weight-efficiency-use issues are actually crucial.
