Thanks rando. The reasons to get a Victron MPPT just keep adding up. I've got the 100/30. Really cold temperatures are not very common in the PNW, but they can get get down to -20' C / 0' F or so, especially east of the Cascades. If the battery goes below 1'C I can disable the DC-DC and run only solar down to -10' C. Charging/discharging should also warm the battery, and once we are on the road, the propane heater can keep the camper warm and the battery above 1'C. I really want to avoid the complexity of a battery heater. I've just swapped the stock 160 W Zamp with 3 x HQST 100 W flexible. Mounted with velcro and with tape on the leading edge - simple, quick and no holes. And now my wife can lift the roof