On a 2005 Fleetwood Excursion with a Cat C7, it's located in the very top right corner of radiator opening looking at it from the rear of the MH. It actually sits on top of the corner of the radiator. It has a black rubber flap (that runs the length of the top of the radiator) partially over it, sort of covering it from sight. Mine is made of white plastic.
Mine recently cracked and caused the low coolant light to come on. If yours is the same, look at if for heat stress cracks and any leaking. It's about $150 for a new tank and a lot easier to change at home than on the road.
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.
