[jleslie]

"It's difficult to tell from the image but if you are getting vertices that are not used in the hull then they are 'inside' the space created by the others."

this might be my problem. I'm not sure how to tell or fix.

"make sure all the surfaces are in the same object and the vertices are shared before combining surfaces (use Object->merge and Object->optimize-vertices)."

tried this. no change.