Hey guys,

Have a look at what I posted in here: http://www.talkcomposites.com/12113/Need-advice-on-how-to-flange-this?Keywords=Flanging#bm12129

Had much trouble with curved flanges. Now I like to use a cheap poster board for flange material, conforms to complex curves easily. I get the stuff that's got a slick polymer finish on one side that's non stick (the regular board I find is too flimsy), then brush a pva on it and tape overlaps.  For fillet, I use, I think it's drywall patch comes in a gallon container and fill zip lock bags, cut a corner out, then squeeze, let dry then pva.  Oh and use hot melt gun to stick the flange to underside of part. The flange does not have to be very stiff, just stiff enough to hold up to firm brush strokes.  Saves time, no cutting or transfering of shapes, just cut strips and go.

You could even do the layup directly on the part and add the flange secondary. 

Sometimes its simpler to just use thin card that will bend to shape, then cover with flash breaker tape. 

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

A method I use a lot for parts with open ends is expanding foam. Squirt some in each end, once cured trim/ sand to shape. Cover the foam in flash breaker tape or parcel tape and use filleting wax to fill the join line. Easy to work with and more substantial than card.
One thing to keep in mind with trim parts is that they often "relax" once removed from the car. You spend ages making a mould, then a nice shiny part to find that it actually no longer quite fits. The same is true when adding flanges, it is easy to change the shape or twist things slightly.