Treating cow skin disease: First of all, remove that horrid lipstick. While cow proportions are good, I doubt the designer ever had stick his hand in a cow's mouth.

What seems to work when exporting .dae from Sketchup, is to:
- Select all and explode all groups/components,
- Repeat until there are no groups/components,
- Use Materials (In model) dialogue to select one material at the time,
- Use Entity Info dialogue and apply same material to both surfaces (in the case off the cows, the reverse side is unassigned).
- Repeat for each material (Model Info, Statistics, Purge unused, makes this easier).

Export the model (without checking option Export Two Sided Faces) and import to SH3D. As far as I can tell, from a very quick rendering test, there is no bleed-through or skin disease. However, I have not checked whether the model contains wrongly oriented normals - and I have not experimented with orienting faces in Sketchup. But at least, it seems the model works reasonably well in SH3D.

ok

PS - there are other ways of selecting all surfaces with the same material in Sketchup too - which is more convenient depends on the model.