A friend and I tried the Duplicolor on my rear bumper cover today. It came out rather light in some places... I'll try to get a picture in the afternoon.
I cleaned thoroughly using some Windex, then sanded lightly with some 500 grit sandpaper and cleaned again. The step strip was taped off, since the primer black would be sufficient and I was concerned that feet, etc would damage the paint over time (should I have painted this too?). One coat of white Rustoleum plastic primer was laid down, and 30 minutes later we touched up the spots we missed with some more primer. An hour later, we laid down the first coat of the Duplicolor and added a coat roughly every hour, and sprayed a total of about 4 coats. There appear to be gray/whitish spots in some spots - were our coats not thin enough, or did we not provide enough time to dry the coats? Like I said, a picture will illustrate this better but my garage lighting is too poor for a good photograph at this time.
If the Duplicolor comes out well enough, we'll probably move on to the front bumper cover and fender flares. I'd just hope it lasts a while - if it starts to flake or fail I'll just shell out for some Wurth and do a quick respray.