Supurb advise on vinyl purses. I have a HUGE problem with making the straps of vinyl as well. It ends up all twisted and uneven. This is how I make them, please someone correct my stupid ways:
First I fold a 4'' * 12'' piece in half. Then I try to fold each of the sides in about 1/4''. Then I try to stitch these together. Not only does this send my machine into overdrive, it also is impossible to keep this stuff folded, and pinning is ineffective. HELP. So, now I just use whatever random things I have lying around (such as neck ties and belts) as straps. I have recently made one with a necktie strap. I will post when I return home.