If you want to be able to inject any character into it, including custom morphed ones, then the dummy will have to have V3's mesh. Theoretically, a dummy could be made which replicated all the standard morphs, but it would never be able to take custom morphs. I don't understand why you can't just use V3 herself? I usually use V3RR for making clothing since she uses fewer resources; but you do need to be careful about her lack of nipples, since a dress made to fit her can suffer from embarrassing poke-through when worn by a full strength V3. ;)