Alsatian, I have been using the Trekker Rectangular bag from Cabelas at a -20degree rating in the CO mountains. I went away from mummy bags awhile back, I sleep better this way. My big deal isn't the bag as much as the pad under me. I am old and crippled up, so 2- 4" foam pads allow me to sleep well. I don't pack in any more, so I can get away with this. And I found cots to be cold, too much cold air under you.
Gselkhunter