I need to create a flange that follows a spline. I want to create a flange so that I can rivet the side panel to the bottom panel:

I know this can be done because I know this aircraft wing rib was created with a flange along a spline in Solidworks:

It would be nice if the flange could have slots like this if there is an easy way to create them:

I have tried to create an edge flange, a swept flange, and a separate lofted flange that is combined and it won't let me do it because I am not connecting planar surfaces.

How do I create a flange on the side panel that follows the mating spline curve between the side panel and the bottom panel?