I generally run warm. I have a little body fat, and a tenancy to sweat, not shiver. With that said, I have never been left on an island where it could rain for days on end (although I hope to be in the future). A few thoughts on warmth… the worst situations seem to be when it rains (and rains, and rains…). I believe using the overlapping split bamboo method, a “waterproof” fire shelter is possible.
The roof has to be high enough to avoid situations that have happened on previous seasons. One of these instances occurred in Survivor Amazon when Butch obsessively gathered firewood and stored it underneath the shelter. This meant that when the fire went awry it sparked the stored firewood in addition to the shelter and the whole thing went up in a blaze. The other instance occurred in Survivor Nicaragua when they put wooden chests containing most of their food around the fire in an effort to protect it from the rain. Needless to say wood surrounding a fire is not the best idea and they too lost items. This leads me to the idea that a SEPARATE shelter for firewood makes sense for a wet season of Survivor as long as it is done safely and correctly.
A fire reflector can be added to reflect heat towards the opening of the shelter. Again, THE WOOD MUST BE FAR ENOUGH AWAY FROM THE FIRE!
Hot embers should also be babied, cared for, nurtured. Protect them in sea shells off the ground and under cover.
Lastly, the idea of “hot rocks” should be explored. You can heat dry rocks (not rocks from a creek, river, ocean, or other body of water as they can explode!). Place the rocks near the fire and when they are nice and hot, they can be wrapped in cloth and snuggled with for many hours on end. Piping hot rocks could also maybe be placed under the shelter, radiating heat up or in the center of the shelter (on another flat rock) as a heat source.
All these things take time and energy, but I believe these things would put my tribe ahead in the game as I can make fire from bamboo easily now. This removes a big time/energy concern allowing for some effort towards “luxuries”.