What is best way to make a flange on curved part?

I am making an enclosure that fits against a curved surface.  So far I created the curved surface, then created an extruded rectange, then cut the curve using the surface.  I was hoping I could use the flange tool, but it doesn't work when face is not square.  I can think of a few ways to do it, but wanted to know if anyone had a slick way.  Below is my test part.

https://cad.onshape.com/documents/c510e7b73cf2c530515236eb/w/33db4cceaa0cd5b9253a12cc/e/8f8f8e62c008dda78151c6cf