I had just bought the -25 from Teton but the non canvas version. It is super warm, very comfy, a little too big to trap in heat especially by your feet. I would feel good if it was around 5-15 degrees out but I think you start getting pretty cold any lower.
Without spending a fortune, throw an emergency blanket under your sleeping bag. I like the Teton Celcius -25 degree. Then throw another emergency blanket over that and a wool blanket on top of that. Insulating your air mattress is key, as you lose a lot of heat out to the ground. Otherwise if you have a high R value air mattress that would work well, like a Sea to Summit ether light XR Pro. But no matter what a really low temp sleeping bag, insulation, and wool blanket or down bivy/quilt will keep you from freezing.
I have a -30 Teton, pad from my hest, and Teton cot. with temps often being 0-20F at night + heavy wind. I am with a large hunting group in a canvas tent with wood stove and propane heater. I used to use a couple bags and blankets that were rated for warmer weather but would still get cold even with all the layers.
Alas-Earwigs
