Modeling Chocolate and whipped icing

Hello,
I’m fairly new to this site and am wondering if I might ask a question. I have an order next week for a cake to be covered in whipped icing. I’ll probably use Rich’s Bettercreme.
However, the customer would like it to resemble a football field with the teams colors in checkered squares at both ends of the cake, with a football helmet and football on the field.

I’m really afraid that if I make the squares or helmet/football out of gumpaste/fondant that they will be ruined from the moisture of the whipped topping.

Has anyone had experience with this?

Or if I make everything with modeling chocolate, will I have the same problem? It should do okay on the whipped icing, shouldn’t it?

Thanks for any replies, I appreciate it.