"Alcoa" style Aluminum rims are an optional upgrade from Jayco. They are not "covers" but actual complete Aluminum rims. You see them often on larger Class A's. They look like these :
Because you can't see the inner dual most people don't pay the expense of having those as Aluminum as well but rather keep the cheaper steel wheels as the inner dual and just run with a plastic spacer between the Aluminum outer and the steel inner.