"CCC" indeed means cargo carrying capacity or something very similar. There should be a weight sticker somewhere in the motorhome that gives the factory weights and chassis capacities and lists the carrying capacity. Often it's in the back of a cabinet or closet. The precise form (and some of the acronyms and math used) has varied over time, based on e.g. whether passenger weight is included in the carrying capacity and similar things. The basic underlying math and concepts have not, of course.
It's a good plan to weigh your RV yourself rather than relying on the factory weights to be correct. This is doubly true if it's used since maintenance, accessories, and modifications can change the weight--usually towards getting heavier.