Greg and Tracy,
We have the same model 2019 3130re and currently on the road on the east coast.
Damn cold outside!!!
1. To verify your tank heaters are working (long answer) you would need to disconnect them and "ohm" them out. Using a multi meter read the resistance of each tank heating pad and compare the readings. Not sure how you would do that without dropping the coroplast. Without a wiring diagram just guessing, (never done it) maybe disconnect the wires on the back of the switch. One will go to 12vdc. The other to the tank heater then to ground (unless there is a relay involved somewhere). To ID which, read for voltage first. Set aside the 12v wire (label it). Check for 0 voltage on the other wire (to be sure) If so, measure the resistance to ground. Make a note of it.
2. Repeat on each of the tank heaters and compare them. Chances all 3 are bad is remote.
Last night in Philly it was 26deg. We turned OFF our fireplace and only used the furnace so it would help keep the underbelly warm. Also had the tank heaters on. I monitored the remote thermometers. Basement inside the convenience panel only dipped to 38deg. We have been filling and using the freshwater tank rather than using a heated hose. Everything was fine this morning. Maybe using the water in this way helped keep it moving and from freezing. Made the mistake of leaving sewer line out last night. It froze. Had to thaw it before I could flush and stow it this morning. Tonight we are in Dumfries. It will be 22deg. We will use the same strategy (sewer line stowed and not used this time
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I have to say the hydraulics do NOT like cold weather. Have to do everything in manual mode.
BTW get remote thermometers so you can monitor underbelly and basement.
To thaw your freshwater tank/supply line, IF your drain valve is not frozen, run a heated hose from your outside shower hot water line to your freshwater drain. Make sure the water is HOT coming out of the hose before connecting it. It will cycle the water from your hot water tank, to freshwater tank and back. Read that on another webpage. Also maybe try putting a couple of hair dryers into the holes around the slides hydraulic rams. Hopefully this will help heat up the underbelly.