Best way to create a curve to fill the gap between fillets

I modelled the object and proceeded to fillet the edges. However at the complex joint between fillets it has left a hole. There are 4 identical holes due to the shape of the model. What is the best way to fill these to create a solid again? I have attached the file and jpegs of the hole

V3 - Option 2.3_Rectangular punch out.3dm (618.6 KB)

Hello - the tricky one looks to be this red surface:

since the blues are not in plane with one another. I made this with a sweep but cleaned up the edge on the U shaped surface first, then Sweep1 and make sure it is matched for tangency - there may be other ways but that is what came to mind. The rest is finicky FilletSrfs and trimming…

V3 - Option 2.3_Rectangular punch out_Maybe.3dm (181.7 KB)