Where is karma stored if there isn’t anything permanent, and everything arises and ceases moment to moment?

We can give examples of how things can continue without any permanent entity, like fire burning wood. It is not the wood, the fire, the space, or the floor that is fixed — everything is changing. But how can anyone demonstrate how karma, habits, and memories follow us? Where are they stored, if they are stored at all? If they are stored, are they unchanging? Did the Buddha give examples of where these habits or karma “stay” and follow us? I don’t see any examples for this. Can anyone describe it? This is something most people struggle with, and people from other religions often question. If there isn’t any solid explanation or way to demonstrate it, then it seems to undermine the idea.