The battery disconnect switch(es) are usually located near the entry door. Sometimes right above the stairwell, other manufacturers put them above the door. I don't think yours is Off at this time if the rear furnace is working. You have two 12v systems in the RV, the chassis battery(ies) operates the driving functions, engine start, headlights, dash HVAC, wipers, etc. The house batteries operate the living functions, water pump, refrigerator, furnace, interior lights, etc. Each have their own fuse boxes in separate locations. I'd find the house fuses and make sure the furnace fuse and all others are good.
The thermostat you mentioned, RVP No 7330-322, is most likely a Coleman brand.
This is a manual for many of their thermostats, you might want to go through the manual for any tests you can use to decide if the thermostat is working.