Hi Roni, can you please post the 3dm model file?

You may need to do something more like model the interior surfaces directly similar to modeling the exterior, rather than actually using the Shell command.

Maybe another possibility for your gap areas could be to cut away a strip between pieces and put in a blend surface between them to make them all one connected skin rather than in separate chunks.

It's pretty difficult to give very good advice when looking at a screenshot instead of at the actual model though. Also another thing that can help is to simplify the model so it contains just some stuff around a particular problem area rather than say a hundred pieces. It makes it easier to figure stuff out.

- Michael