I use the steel clean canteen bottles for the dual purpose drinking/ boiling water use as well. In winter time I use a boot liner to stuff the hot bottle into a little before bed to warm up the hammock. then I keep the bottle between my thighs, which seems to work good for me. I have thinsulate boot liners from the army surplus which hold the heat amazingly. By morning my water is still warm.
I just learned about this trick last winter and It works great for me.