I heat 100% electrically. Propane is a back up only. I use oil filled, radiant, electric carpets, and fan based heaters. This has been tested to -36 C (-33 f).
Inside the living quarters:
750 watts of carpet (3)
1300 watts of oil filled heaters(3)
284 watts of radiant (1) my favorite
1300 watts fan based (1)
1500 watt heat strip (set below room temperature so if outdoor temperature cause RV temperature to drop it will cut in)
15 watts fan only to "push" air through the duct work (1 dual window fan)
1 220 volt 100 watt light bulb that lives by the water pump
(last two items on a mechanical thermostat)
Outside living quarters:
1 electric carpet 250 watts pass through storage on a thermocube TC-3
1 fan based 600 watts in enclosed waste tanks area on a mechanical thermostat
1 200 watt heater in hose storage compartment (switched from inside RV)
1 60 watt bulb to protect the fridge from freeze up on a thermocube TC-3
Not all of these are active at the same time, except when I pull the RV out of storage in mid winter.
No extension cords are used from outlets to heaters. I do have two auxiliary shore power cords of 20 amp and 15 amp to supplement the OEM 30 amp.
I would recommend upgrading the 120 outlets to anyone using more than about a 600 watt item.