As someone who camps all Winter in Maine, I've never felt the need to heat a tent.
1. Eat before bed. Go to bed warm.
2. Get a good quality sleeping bag, or quilt. Manufacturers temp ratings are survival ratings, not comfort ratings. If a sleeping bag is rated for 30 degrees F, you'll be lucky if you're comfortable at 45 degrees F.
3. Fill a water bottle with hot water before bed. Not hot enough so it burns your skin, but hot enough to be uncomfortable to hold. Wrap a towel around it or put it in a spare sock and sleep with the water bottle between your legs.
4. Sleep in base layers. Sleeping bags and quilts are tested with the assumption that the sleeping person is wearing a hat and base layers.
5. Shake out and fluff up your quilt or sleeping bag. Being in a compression or stuff sack destroys the loft needed to keep your body warmth inside and not leaking out into the cold.
6. Be aware that compressing synthetic bags permanently destroys the loft of the fibers. Older the bag, the less warm it will be. Stick to down for maximum warmth.
7. Stack quilts or sleeping bags on top of each other, or inside each other for extra warmth.
8. Drape your jacket over your sleeping bag. Avoid crushing the loft in your bag by draping heavy blankets over you.
9. The insulation under you is as important as what's on top of you. Have an insulating layer under you.
10. Cuddle with your partner. Share that body heat.
