Need to get your RV Battery charged........either by using a portable battery charger or via jumper cables to your vehicle
Portable battery charger better method. Just plug it into an outlet (even one on tt) and connect to your tt battery.
Then you can keep battery charged, use the battery for DC power until you can replace your converter.
With a charged battery furnace will operate, Fridge will operate, water heater will operate (Furnace uses ALL DC, Fridge/water heater can operate on AC but need the DC for controls----if water heater has electric element)