This is an interesting thread.
I have an issue that seems similar. I bought a drop-in LiFePO4 starter battery replacement for my motorcycle. Works great in the summer. Seems like it discharges in cold temperatures. I was assured when I bought it that it wouldn't have any issues with cold. Absolutely false! Around 40F or less at night, and the battery is dead the next day. Like around 10V dead.
I keep mine on a LiFePO4 maintainer/charger when the weather is cold. Seems to work fine. I'm not sure if it keeps the battery warm, but it at least is fully charged, (13-ish Volts) and it will turn the engine over fine. I don't know if maintaining the battery at cold temperatures would be causing damage or not.
I suppose another way to keep the battery maintained in the winter would be to somehow make an easy disconnect and keep the battery indoors when not in use. That would be pretty inconvenient though if you use it everyday. I've also got a LiIon battery booster to "jump" the battery when I forget to put the maintainer on. Works good in a pinch, but the maintainer is really better.
Not sure if any of that helps, but that's been my experience. I look forward to seeing your test results.