Phil, I feel your pain. I also have the Expion 360 VPR system (installed 3/2020) Gen 1. The Gen 1 BMS does not prevent charging below 32 F degrees. The Gen 2 series do ....
As you probably know, Expion does have a battery wrap available, but again, no thermostat,
Thermal Wrap EV-V120-TW $78.00ea (1 per battery).
Master 20A switch EV-BHS $10.00ea (1 per 2 batteries).
Price includes shipping.
Heating Element Link from Joel at Expion =>
At present, I’m going to use a small ceramic heater under the platform bed at night if the temps are in the 30’s when the van is not in use. We have a Truma-Combi Eco heating system that will likely work for us while we are traveling and using the van in colder weather. Fortunately, being in AZ in the winter is a good thing, except if you love to ski. Unfortunately, it looks like this winter will be the second winter that I have been kept off the slopes due to the pandemic.