Well despite its size, I imagine a dosuyukkuri would still be relatively soft. I mean, it is just a giant manjuu, after all. A missile could easily rip straight through a layer of hardened dough and beanpaste.
Also, missiles generally do not arm themselves till they have flown for a set distance. This is to prevent them from blowing up their launcher from an accident or some such event.
Plus, certain missile types will not detonate till they have penetrated through a certain amount of armor/bunker layers/what have you, to maximize damage. Tho that is typically used in AT Missiles, and Bunker Busters.
And I just realized, with that hole though the DOS, I'm sure someone's gonna do one with the line "This is my hole! It was made for me!"