tatest explained it great. If your RV uses flexible conduit to route its heat, then it should be trivial to open cabinets and see them. They will be about 3" in diameter and look like a big covered slinky or the hose that your dryer at home hooks up with. These hoses just slip over fittings at the furnace end and the vent end and generally don't have any clamp or anything holding them on, so it is possible one has been pulled loose.
The owners manual does state to turn on the propane to operate the "furnace". I assume furnace is the same as "heater".
Furnace generally implies burning something to make heat.
But I'm a little confused now as to which heater you are talking about. Most RVs have a propane furnace. It requires 12VDC to make the fan blower work and of course propane to make heat.
However, some RVs have electrical strip heaters in their roof AC unit. When running on 110VAC, you will be able to get heat from your AC unit.
I think you are talking about your RV's propane furnace duct work. Almost certainly the duct has pulled loose at either the vent end or the furnace end.
Now there is one more possibility. My RV generates cabin heat using engine heat when driving down the road. But that fan only blows out under the kitchen table and the fan motor is controlled from the dashboard up front. Under my kitchen table there are
two vent outlets. One is from the engine heater core and the other is from the propane furnace. My propane furnace has ducts that go to under the kitchen table, into the bathroom, and into the rear bedroom.
Steve
1990 Winnebago Warrior. "She may not look like much but she's got it where it counts!"