After struggling to figure out exactly how to model each piece for 3D printing, I decided to build a prototype out of clay & foamcore.
I’m using this cool flexible rod (intended for hair, apparently) as the spine:
Fashioned the spine out of foamcore pieces (to attach the back plates to) and modeling clay (to function as the interior body)
Haven’t yet figured out what to use for the belly/legs, but here it is!: