OP wrote:
But where do you take the measurement on your truck?
Most trucks that are approved for camper hauling will have a booklet listing the points of measurement to determine the longitudinal position for the COG point of the camper. This range of distance varies according to the trucks configuration, ie; cab type, seating type, engine type, etc. Use the info in the booklet that comes with the truck or find it online from the manufacturer. Anything, else is just guessing.
ryoung
I no longer own the truck and TC in my signature.