* As I wrote down on the Wiki, that happened to me when the mesh had bones with zero weights. And it isconsistently happening when the meshes have those extra bones, and the meshes become visible after removing them. I haven't had any other causes for invivible meshes. * If you want it to keep its form, rig it only to one bone, for example, if you want it to follow the head, then paint all the mesh with a weight of 1.0 (100%) for the head bone and delete the rest of bones (vertex groups in Blender). The stretch is due to different bones moving in different directions and parts of the mesh following the movement of one of the bones and other parts of the mesh following the other bones. * I don't know much about Outfit Studio * I dont understand what you mean by "skeleton rigging". You, of course, need to attach a skeleton to the mesh before exporting it from Blender. The tutorial on the Nexus Wiki explains how to do that, but if you have any further question, feel free to ask ;)