Is there a way to select all the outside faces only so I can apply a different shading domain/material from the inside faces?
Select any face on the outside surface and hold down your “shift” and “+” keys. This will cause your selected face to “grow” to cover all contiguous faces.
BTW, if you ever need to work on only the INSIDE geometry, you can do the same as above and then hide the selected outside faces.
Damn, Roy!! I saw your image and your “like this?” comment, but I swear I didn’t see your instructions below that! I think I must be going daft…