I have no experience, but would suggest 5 and 10 degrees C. The closer to 0, the more you should restrict charge rates. Just a suggestion.A little update.
Had a message from JBD that stated "The heating pad has a power of 100W @ 12V Max 10 A at low temperature"
I have ordered two 10W silicon heat pads that i will place on some foil bubble wrap (under the cells) to spread the heat more evenly under the 4 cells.
I plan to set the heat pads to turn on at 3C and off at 6C, so the cells never get close to 0 degrees.
My battery build is going in my van so the cells will be inside a plywood box and insulation underneath plywood box.