As far as I can tell bodypaints and second skins simply put aren't much more than a texture. Personally I do all my textures in Adobe Photoshop CS, other paint programs are out on the market as well such as Coreldraw and PaintshopPro. To do model texturing you need a template for your model, this shows exactly how your model is mapped out so you can fill in all the right places with your own textures. You can find a lot of templates right here in the FreeStuff section under textures or utilities. Hope that helped a little with your question.