What's the best way to 'mark' a SM part before going flat?

I'm new in SM-land, but after attending Gerald & Wayne'ssessions at SWWorld, I'm not as intimidated.

I'd like to add something (lines, surface edges, etc.) in the bentstate that will translate into the flat for the purpose of locating(dims on dwgs) items during assembly.

As you can see from the attached pic, the line locations are notalways equally spaced around the curve. This is for plate work, butI'm sure someone has tried this in SM.

I've tried creating surface breaks with planes, but encountererrors going flat. I've also tried split lines, with no success.

This is part of a large duct, and stiffeners will be added. Itwould be great to mark the stiffener locations when designing 'asbent' then have accurate placement markings in the flat.

Cheers!SolidworksSheet Metal