The freshwater tank in our coach appears to sit over/between the two frame rails and is nearly impossible to see unless the two living room slides are open. Of course, if you crawl under the coach, then its bottom is likely visible. I don't know... haven't crawled under there. I assume the tank is plastic, but I cannot see it. There appear to be two vertical metal(?) sheets fixed at their bottoms to the outside of the frame rails that encloses the plastic tank on the tank's left and right sides. There appears to be a bit of clearance between the diesel tank and freshwater tank with the generator, diesel tank, and freshwater tank lined up front to back in series. Interestingly, all three appear to be roughly that same width and are located on the exact centerline of the coach.