I tend to trust Andy's advice, but I also gotta mention my own experience with an under-truck fuel filter. My truck has one placed where the fuel line was cut to plumb the 3-way switch for the twin saddle tanks. It was like that when I bought the truck, and I never saw the need to change it. In 28+ years it has never caused me any trouble - I just change it every few years or whenever I think of it. YMMV
