I think that 99Win... is mixing up the water heater and furnace, they are slightly different.
Furnaces do not use the pilot light system. The power required is the normal 12V supplied by your battery. None I am aware of use electric heat. If you have lights, you have power. If your gas stove lights, you have propane. (Always a good idea to light the stove for a few minutes first though!! This will tend to remove any air trapped in the propane lines which hinders the lighting of a furnace (or a fridge)).
Furnaces have a DSI ignition (Direct Spark Ignition) system. Select Gas Heat on the thermostat, set a temperature 2-3? higher than ambient and you should here the noisy furnace fan start. Less than a minute or so later, you should hear a low clicking sound from the furnace. (This is the DSI ignition). When the furnace lights it sounds like a low roar and hot exhaust should pour out of the exhaust outlet outside. The furnace will try three times to light, if it fails it will shut down and you have to reset and try again.
For the water heater, if help is needed there, to steer you straight, we need the make and model of the WH..... Some use DSI ignition, some a pilot light. Some have the electric heat option as well as gas heat but the water heater HAS to be full of water before trying the electric. It also requires the trailer be connected to a 120V AC supply.
HTH