Hi,
if you know how to skin for any sim, skinning for cfs3 is not any different except for
- the format used. DDS DXT1 is the most common one used. (there is a thread here about dds - search for it).
- the use of specular textures : these textures are greyscale and they define the amount of shininess of parts, which can be of great use to weather a plane very realistically.
Maybe you'll get more information at the two most active cfs3 forums :
- http://www.sim-outhouse.com/
- http://forums.netwings.org/forums/index.php