Davis,

Your description of the problem is a bit strange. The model you are linking to is a SKP model, not a ZIP/DAE (=collada) or 3DS model.

There is a known problem with collada models: the orientation of faces (what you call skins). Think of a sheet of paper having two faces. The render engine used by SH3D (=Sunflow) has a problem deciding which face to show.

You can solve this problem by importing your model into Sketchup and then using the function Edit --> Face --> Reverse faces. You then have to use File --> Export --> 3D model to export the file as a DAE model that SH3D can use.

Hans