yeah maybe the OP wants Cool Whip specifically because it lasts longer as a cake topping versus whipped cream? I'm not even sure if that's true, as I haven't used it for that purpose, but I think it might be.
I've used regular double cream, whipped with vanilla (and a bit of sugar) as a cake topping, for a Tres Leches Cake, and it held up rather well over the course of the afternoon. Better than I thought it would, anyway.