Hi ASharpCanadian,
I do quite a bit of winter camping here in the near north of Ontario (mostly in snow shelters and occasionally in tents) , but in either case what will make the greatest difference to your sleeping system in cold weather is your under-padding. A good winter bag, no matter how much you spend, will not keep you warm unless you have plenty of insulating distance between you and the ground, which is an endless heat-sink. Even the best sleeping bag, when you are in it is compressed completely flat by your weight, offering you negligible protection from the cold. So, you're wise to ask about under-padding. You need lots of under-padding. A typical Therm-a-Rest by itself will not suffice, but there's no need to buy a special winter pad. What I use is an ordinary summer Therm-a-Rest pad (the Prolite 4) combined with one of the thicker closed-cell foam pads. A closed-cell foam pad is cheap; around 20 to 25 dollars from any camping store or Walmart. I got mine at Canadian Tire. Just don't get the very thin ones. Get one of the thicker ones they have. Neither a closed-cell foam pad, nor a summer Therm-a-Rest pad, by itself will provide enough insulation against the endless heat sink of the ground, but the two together will make all the difference. Alternatively, a big piece of Reflectix duct insulation will also work well in place of a closed-cell foam pad, though this material is costlier and the silvery coating will eventually wear off, especially when laid out directly on snow.
In case you're interested, I have a number of videos on my YouTube channel about cold-weather camping and I even have one video where I show how I dealt with the problem of inadequate under-padding when I got lazy and decided not to bring enough under-padding.
Good luck and I hope your girlfriend enjoys herself out there.
Hope this helps,
- Martin
