I came by chance across this interesting item on SL Exchange: AvPainter – SL Clothes Design and Preview Tool by Pootle Trollop.
I don’t have Windows, so I haven’t tried it out, but the author claims it’s possible to upload a .tga file for your clothing and apply it visually to a polygon mesh representing your avatar (this mesh is freely available from Second Life’s website). This should be able to preview the way the clothes fit in a much better way; and for the cost of around US$10, it’s definitely not an expensive tool to have if you are seriously interested in doing perfect-fitting clothes and tired of doing it “the hard way”, that is, uploading to SL, spending L$10, watch if it works, tweak it, upload it again…
You can download a demo of AvPainter here.
Great work, Pootle 🙂