Hi Dan, yeah cutting off the curvy bits makes for a more simple structure with fewer surfaces and edges in it.

I've done some surgery and reconstruction on your object and attached the result 3DM file here - I basically removed the curved corner pieces and instead moved the control points for the other curves together to make sharp corners and did some rebuilding of the side piece.

This version will now shell up to about 0.1 units, after that the little bottom narrow part will collapse so the shell is limited by the thickness in that bottom area of the model.

After doing a shell of 0.1 units and then cutting away a piece, it looks like this:




Both Shell and Fillet tend to be rather sensitive operations, if you want to use them you kind of need to plan for it a bit and try to get the model set up into a more simplified state (have stuff like a clean edge structure, no little tiny surfaces or fragmented edges, etc..) to give them the best chance.

- Michael