Hi Ed,

I just extruded the profile of the shape, then added a fillet.

When creating the profile use 2 continuous freeform (control point) curves, one for the top of the profile, and one for the bottom, make sure they connect at each end. Then select both curves and extrude. That will produce continuous surfaces on the top and bottom of the profile which will then allow filleting.

I have attached an example of the profile curves (I dont have the curves for the model I posted, so have just quickly made them again), just select them, extrude, then try different fillet sizes (start small under 1)