The TT or ST (Rear twin bed) models have enclosed and heated holding tanks. and do not have Tank heating pads... In cold weather, the furnace supplies the heat for the tanks. Using a space heater will not. There is a duct from the furnace that runs under the toilet platform and into the holding tank compartment. Keep thermostat comfortable inside and tanks are protected.. Your water bay is not heated and in cold (below 25) temps I put a 100 watt light bulb in a reflector in the water bay.
FWIW, the heating duct that runs forward on the passenger side to the stepwell, runs behind and alongside the fresh water tank under the bed and keeps that area warm.. (When furnace is running)
The other Siesta/Synergy models have exposed holding tanks under the RV and do have electric heating pads.
U.S. Coast Guard retired- 1956-1985
2016 Siesta 24ST
1972 Moto Guzzi Eldorado