I notice that some here are into using heavier gear in winter than one might expect to find on a light bping site and Tom, at least, needs a heavier bag for colder weather.

It is not really necessary to use heavy, bulky gear in severe cold as IF you can buy the best, it iS lighter and WILL keep you warm in awful conditions. I do not have time right now to do a full list, but, have solo camped in the Kootenay mountains for nearly a week at a time, in temps. recorded to -41*F. In that very damp area, that is truely miserable cold, believe me!

I will recommend a couple of bags for Tom and anyone else interested and some pads as well. I use Evazote under my Exped 9 Deluxe or my Big Agnes Ins. Air Core and the best one I have is a "Roots" in dull black, from Canadian Tire, of all places. It is softer, wider and thicker than most and works very well under the above. I add Gossamer Gear Torsolite pads over it and then my inflatable pad. This is one place where I do believe in carrying a bit more weight to keep warm and can, as I have no fishing gear, hunting stuff or whatever with me and thus am a bit "lighter" over-all.

For a bag, the absolutely FINEST I have EVER had is my Valandre Shocking Blue, good to -15 or -20 and only THREE lbs. total weight. I also have WM, FF, ID and other bags and had an original Marmot Mtn. from Grand Junction and the Valandre beats them all. If, you want something for even colder weather, they have "expedition" models and the WM "Bison" is a fine choice, almost bought one before MEC quit stocking them.

Spending serious coin on a top bag and clothing is worth it for cold camping and being able to be comfortable without a fire is also a wise move, just in case you injure yourself and cannot collect wood. A MSR naptha stove plus Ti pot is a good thing to have for this as well.

Look into Valandre, the bags are just amazing.