— Shivering Ethan, Esmond, R.I.
A. Since I don’t know everything about your situation, Ethan, I’m just gonna have to give you some basic advice.
If your sleeping bag is a basic rectangle shape, try a mummy-shaped bag instead. Those fit closer to your body, so there’s less room inside the bag for your body to heat up. The fleece liner is a good idea, as that can add some valuable extra warmth to your bag. You might also try sleeping in your clothes, and wear a stocking cap — lots of your body’s heat escapes through your head. Maybe try a down sleeping bag. No synthetic insulation can match its weight to warmth ratio (but it’ll be more expensive).
You mentioned your 20-degree bag not being warm enough. Those ratings are just a general guide to what temperature you could sleep comfortably in. If you’re a cold sleeper, and it sounds as if you are, go for a sleeping bag that’s rated for much colder temps, like a 0-degree bag.
Finally, make sure you are sleeping on a sleeping pad, because the cold ground can quickly suck valuable heat from your body. Much like sleeping bags, pads are rated for colder temperatures, and using one would definitely help you sleep warmer.