Hi Richard, cool models! Sorry you are having trouble with the uploader. I have not tested it since last year...Shapeways may have changed their API. Also it may just have been still uploading - it can be slow if you have a large model.
I will have a look at it, but probably you are better...
Using the meshmixer Transform Faces tool (select some faces and then go into Edits menu) you can incrementally build a void from the outside in (so there is always a way for the material to get out). It will be a lot easier if you use the transparency shader. And you can get a nice clean...
Well, one nice thing about meshmixer's Booleans is that if they fail, they are just going to leave some small holes at the join region. And you can fix those holes with...the hole filling tool in meshmixer! =)
There is also a tool called the Inspector that will point out all your holes and...
You might check out the newer versions of meshmixer, I've put quite a bit of other stuff in beyond the initial mesh drag-and-drop tool. For example it has an extensive set of dynamic-mesh sculpting tools, and you can go up to 5-10 million triangles. And Booleans, hard-edge tools, etc. Have a...