I doubt EVA foam will “stand up” in a box form factor. The sides and the top will all cave in. It works fairly well on those Crocs is because it isn’t exactly EVA foam, it is nice and thick, and it also uses the shape of the arch.
Again, I don’t want to be a jerk. But this sounds like saying “I want to make a prototype that is exactly like a Bic pen”.
It will end up costing you hundreds, if not thousands. It will take up hours of your time. The first one or two prototypes won’t work. If you have money and time that are 100% expendable, it could absolutely be a fun process though.