Condensation on upper inside walls ral cold morn

Though the De-Humidifier does kick some heat into the house (Note the watts on the id tag and do the watts-BTU math same as if it was a heater).

It is basically an air-conditioner.
Sucks in warm moist air over evaporator coils.. Same as your A/C does. then passes the same now cool dry air over the condenser coils. (The A/C has the condenser coils outside and uses outdoor air on them. passing the cold air back into the RV.)