CAN THIS BAG BE TRUSTED TO -20 WHICH IS...
CAN THIS BAG BE TRUSTED TO -20 WHICH IS PROBABLY GOING TO BE THE TEMPERATURE FOR 4 DAYS?
Brian. Seeing as how this is a -30 bag... I would certainly hope that you would be okay at -20. Also, if you are in a snow cave or a tent it will be warmer inside than the ambient outside air and you should have nothing to worry about. Now, if you are sleeping outside without shelter at those temps I would suggest a different hobby! I hope this info helps.
I wish you could trust ratings. Look at these reviews for this North Face Dark Star -40 bag (dubiously cheap for a -40 bag) http://www.trailspace.com/gear/the-north-face/dark-star/