Step 7: Planning the internal structure & prototyping!
We did this by making a new Generic Revit family, and then nesting our skin model into that. The 'traditional' family editor in Revit is a little easier when it comes to solid-style modeling like this, or when dealing with assemblies of parts. We tend to work in this way often anyway, so it is faster for us than using the more complex mass editing.
One thing Revit is awesome at is making really smart models. I was able to make a parametric 'hole' family, just a cylinder really, that represented where a bolt hole needed to be. It would remain 'true' or 'normal' to the surface, even as I dragged it around, so I could place bolt holes evenly on the complex skin panels really easily. I could then join that 'hole' to the skin, and get perfect holes in a complex surface just where I wanted them easily.
Once we had what we were now calling the 'bulkheads' modeled, we made some prototypes! We try to make them as soon as we can so that we can test our assumptions and ideas as early as possible. It's very easy to make 1/2 or 1/3 scale prototypes when working with digital fabrication. The prototype really helps to bring up problems early, when there is still time to do something about them. We cut the bulkheads out of plywood, slotted them together, then cut the skin from a flexible PVC plastic sheet and just screwed it to the frame with small wood screws.
After looking at the prototype, we tweaked the final model just a little bit, and it was ready for the next step...