I'm not sure where the filter is on your particular trailer, but, FR usually puts them very close to the water pump. If you can find your pump, the filter is usually there too. You can find the pump by following the noise. Often, you will find them behind a cabinet door with hinges on both sides. Just take the screws out of one side and open the door. If not behind a cabinet door, then look behind any false panels inside cabinets or outside storage compartments.
John & Nicole
2004 Ford Excursion 6.0L 4x4
2011 Flagstaff 831FKBSS
Nights Camped: '06=122 '07=12 '08=18 '09=10 '10=18 '11=28