I would just use Maple as your material. One of the cheaper woods but you can make it look really nice. i would say use MDF but most of it is not water proof. But if you could get your hands on some water proof stuff i would do that then get whoever gets it to paint it how they want to it can match their gun ext. Keep in mind that MDF is also heavy as hell compare to most wood. all this being said if you get some mahogany ill take whatever you make. That or walnut
Everyone else had good ideas on what to make so i wont say much about that. Should also ask what kind of CNC is it? do you have multiple bits? That can do different things?