In our 2004 Country Coach each AC has it's own filter. In the ceiling there are clips in the return air by the vent. Press the clips to remove the cover for the filter. The filter is foam. You can either buy larger foam filters and cut them to fit or you can order the filters from RV suppliers in packages of 2. You can also wash them gently (they will stretch easily) to extend their use.
Lonny & Diane
2004 Country Coach Allure 33' "Big Blue"
Towing 2008 Chev Colorado 4x4
Semper Fi