If you have a 2004 unit, then you have a newer all electronic ignition furnace. As Steve stated, once the T stat calls for heat, the blower should run a purge cycle. Then it will attempt to auto ignite the gas, if it is firing and you listen real close you can hear the constant sparking sound and the clunk of the gas valve opening.
And to the sail switch, Yes, yours has one and your camper must either be plugged into shore power (120VAC) and the power converter working or if running on battery only, have a well charged battery to create enough power to run the blower hard enough (fast enough) to close the connection on the sail switch. If the voltage it too low, the blower will run and not much else will happen.
To help you better, we need to know what the furnace does or does not do once you turn on the T stat and the call for heat is above the current temp in the camper. Does the blower run but not ignite or do you not ever get the blower to run?
Some answers to 2 questions helps point you to the next steps.
Hope this helps
John
PS. the sail switch in the newer Atwood furnaces is buried deep inside the blower housing. It is not easy to change. However if you are electrically handy, a volt meter can tell if it is closed to rule it in or not.