On the Fleetwood Discovery and Excursioin model, they hid it behind the water control panel on the driver's side. The panel goes about half the way down from the top to the bottom and all the way accross that compartment. You have to get down on your hands and knees and then look up behind the panel. If that's where yours is, don't over tighten when replacing the filter because there's no way to get a filter wrench on it. Use some vasoline on the o-ring and then just tighten it enough so that it seals.
I'll bet some of the people that designed the MHs read these forums to get a laugh out of the difficulties that some people have.......
Bill
Nodwell RN110 out moose hunting. 4-53 Detroit, Clark 5 spd, 40" wide tracks, 10:00x20 tires, 16,000# capacity, 22,000# weight. You know the mud is getting deep when it's coming in the doors.