Select all the geometry.
Use the Fredo6 extension Joint PushPull.
Select all with the component open for editing (why is it ‘double wrapped’ as a component within a component?)
Start JPP and drag inwards.
Type 2mm (it will enter in the Measurement box).
Press Enter to start the extrusion.
That gets the shell 2mm thick. Or should. But I got an error and the extension didn’t work.
Tried again using the Thickener option.
That ran to completion, but didn’t work properly either, but looks as though it might be fixable.
I’ve done that, and saved the result here:
shell.skp (436.5 KB)
Until I copied your model into one with a plainer style, I just couldn’t see whether the initial result had worked.
Can you tell from this view? And that’s after I had set the view to Monochrome. Maybe you are used to this colour scheme? Or it’s in Dark mode, which I have neither used nor seen before?
Looking again, and assuming that black is a front face, and purple a back face, then I can begin to see the problems.
Compare with this:
I can see more easily here that it hasn’t worked well.
Open the component for editing, and Move/Copy the bottom face up to the top, reverse faces, and delete the excess lines that are in plane.
Sorry, it’s late, and I haven’t time to see if that works except for briefly trying it on the bottom face.
To round the edges, use Fredo Corner extension.
Both extensions need you also to install FredoLib.
To round edges, select them, then start Fredo Corner, specify the rounding radius and number of segments in the round.
To make that bit work, you might do better to use the Dave Method (search this forum for it) and scale up a copy x 1000 first, Zoom Extents, then work on the scaled up copy before deleting the large copy, and use Zoom Extents to see the result in the original.
I’ve left that for you as I don’t know how fine to make the segmentation. I did try it briefly on the marked edges, using 0.5mm offset and 2 segments. It seemed to work, but you will want to fix the Joint Push Pull operation first, I think.