Hi Dimitri, so this might not exactly apply to your specific case since you've got a thin design that might not have so much natural "extended material".

But for many cases instead of building this which then needs to be filled:


Instead build this extended solid and a 2D side profile curve:


Then you use boolean difference to cut the solid with the profile:


That automatically produces the "fill" by the extrusions of the profile curve without needing to do any extra steps:


- Michael