I have made a duct tape double using the threads instructions and it was servicable, but not fantastic. I am "curvy" in many areas and the duct tape turned those curves into lumps. I then found Jean Haas dvd's (Clone Yourself a Dressform) and found her very detailed instructions to be the key. She shows the order and method for taping over curves, "inbedded waists"
i.e. love handles, bustline, shoulder caps, etc. Her method was remarkably more effective and included how to make a stand or use an old form, how to stuff and how to mark the final form. Well worth the money if you do much sewing for yourself.