Instead of hollowing in Meshmixer, you can have Netfabb do the hollowing. Strictly, you would have Netfabb create a new part, then combine it with your original part in some way to arrive at your properly hollowed part.
Presuming you to employ Autodesk Netfabb Standard (30-day free trial, or paid subscription), do:
1. From Extras menu (main menu or the part’s context menu), pick Create Shell.
2. In the pop-up, specify the mode of creating the new shell (technically, it’s a new part). Your options are:
a) Hollow Part - generates a hollowed copy of your original
b) Inner Offset - generates a shell that is “leaner” than your original
c) Outer Offset - generates a shell that is “fatter” than your original
d) Hollowing Shell - generates a shell that is “leaner” than your original, but with all its faces turned inside out.
e) Hollow Part Improved - generates a hollowed copy of your original, like a, but with a fancier algorithm. See which one works best for you.
3. Specify shell thickness and click OK.
Depending on what option you chose, you should then:
For a or e, continue to work on the generated model,
for b, use Boolean Ops to SUBTRACT the created shell from the original,
for c, … undo and pick the right option next time,
for d, use Boolean Ops to ADD the created shell to the original. Alternatively, use Merge Selected Parts.
(Part: An individual collection of one or more shells. Shell: A collection of one or more triangles, adjacent or not.)