Preferably print with PETG as it is more water resistant.
Put the InnerCower in place before pouring on the ice, as it is easier to get the ice correctly placed. Once the ice is placed, remove the InnerCower and put on the TopCower.
Preferably put crushed ice inside and put it in the freezer until you need it. If you pour water inside to freeze it, it may crack.
Use 2 magnets to hold the InnerBox in place and so it does not float up when the ice melts. See the picture.
You can also add a little salt to the ice to get an extra low temperature. Do not put on salt until you are ready to use it, as otherwise it will have no effect.
With the InnerCower in place, you are ready to pour in ice:
The author hasn't provided the model origin yet.