Apparently it won't let you do a shell thickness less than 100nm. One workaround is to scale the model up, say by 100. Then shell with a thickness of 800nm. Then scale down by .01. However the thickness is so small at that point that I can't guarantee that there aren't problems with it after the scale down. There are no errors or anything, but it's just that at max zoom I still can't see the thickness.