After HT explained it in another thread I now know a bit more about the way AH converts the skin files we submit.
For embedding a skin into a terrain you should have at least the specular map to go with the diffuse map, that is if you don't want the skin to look way too shiny in the game. This specular map could be just a blank dark grey bmp if texture size is an issue, as one colour bmp files compress down to only a few bytes when built into the terrain. Blank files for the skin's other maps would be fine too. A full set of blank files would give global levels for the specular, power and environmental effects, with no bump effects. This is pretty much the same look as before bump and spec maps were introduced into AH2.
