On my '98 Allure, it's in a box on the middle rear wall of the third bay back. Mine is only accessible if you crawl into the bay from the passenger side and unscrew 4 screws. It was such a pain for me for changing filters or winterizing, I removed the filter housing completely and connected the inlet and outlet feeds with a permanent coupling. I now use that same housing as an external filter on the supply hose. Much better for me - YMMV.
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1998 Country Coach Allure 36' (CC# 30146), Cummins ISC 325
2012 Jeep Grand Cherokee Overland, Roadmaster Brakemaster & Blackhawk