I have a 2007 37' Allure Sunset Bay and a door in the plumbing bay labelled to access water filter, but alas, no filter installed. I attribute it to the smaller (?) plumbing bay space and it was not installed at factory. Mine is discussed in my Allure operating manual, written for all Allures.
Towr: 2007 Country Coach Allure 470 - 37 Sunset Bay Cummins 400 ISL
Toad: 2016 F150 King Ranch - 3.5L EcoBoost 4x4 Supercrew (curb weight 4,775 lbs)
Toad: SOLD 2007 Jeep Grand Cherokee (yes, it has a Hemi) (curb weight 4,720 lbs)