How do I shell this?

 From:  renklint
1402.1 
Hi everyone, having a good time checking out MoI. The only 3D app I've tried before is Sketchup, and some things were a bit strange in the beginning, but the more I learn the more this seems intuitive.

My problem is that I try to do some different models that I want to give some thickness. This particular model was made by drawing some lines and then loft them, the resulting model was then mirrored. Then I used the shell-function. I tried normal and flip direction and realized that I needed the centerline direction. As you can see it didn't create a shell at first until I picked a smaller thickness.












But the result is a bit ugly in some places. I did try a boolean union first, but that made it worse. Any ideas how to correct this?

/Lars