I found the original to be not watertight, the main areas were the sharp loft on the eye sockets and nose areas, I have smoothed these out in blender whilst keeping the overall look of the model intact.
Now Mesh Tools doesn't flag this as not watertight in Cura.
Currently printing @300% scale
Simple_Skull_Container_Halloween_Deco_revE.stl | 994.9KB |