Each object in Blender becomes one mesh prim in SL. If the uploaded model has multiple objects, they will be uploaded to a linkset (or a coalesced object if they exceed the linking rules).
I did notice that. happening
Each Blender object can have up to 8 materials assigned to its faces. The collection of mesh faces assigned to each material becomes a "face" in SL. The naming of the materials is ignored, but their order determines which corresponds to which face number in LSL scripts.
Ok, this is where I often found trouble with while uploading my mesh avatar, and indeed my mesh clothing. This is why I went with the objects/linkset option but that did not work out well, since it left visible creases.
Although an object can have multiple UV maps in Blender, and in Collada, the SLuploader will only use one. Therefore you have to ensure that the right UV map is exported (most simply be having only one). This means that the UV mapping for all materials must be included in the same UV map. It does NOT mean they have to be non-overlapping, as the parts used for each material will be used in isolation for the texture applied to the corresponding face in SL. Making the UV mapping of the materials non-overlapping wastes UV space and limits obtainable texture resolution needlessly.
Let me get this straight. Only one UV map is used, and the UVs can and should be overlapping, which can be done by selecting the polygons and unwrapping them as if they are separate objects for maximum UV effency . The SL faces are the texture maps, who's names are discarded in favor of face 1, face 2, ect. Up to 8 of such faces are supported. So I could have the head, body, legs, plus 5 more faces. Now, how do I find the face number?
Also, how would I go about combining my UVs in Blender? When I join meshes the 3 UV maps are also combined, as separate UV maps on the same object. I worked extra hard to get the the UV maps sl compatible and do not wish to loose all that hard work