Thanks for the "heads up". I'll experiment with the aluminum bottle under the hood this winter. Even though it will still be frozen some percentage of the time, it would be nice to at least have a chance of having liquid water.

FWIW, I sacrificed one of the Nalgene bottles to the Norse God of Ice last night by filling it and sticking it in the freezer. Seems to be holding up ok, but there's still a small bit of water. If I keep the Nalgene bottles in the truck, they'll be in a plastic bag just in case...