How do I fix these manifold issues? And, should I have to "fix" the model in Simplify3d every time, or can I address that in Blender? (Blender -> Simplify3d) : r/3Dprinting
modeling - What is non-manifold geometry? - Blender Stack Exchange
Mesh.IsManifold returns true for non-manifold meshes - Scripting - McNeel Forum
Non Manifold Geometry Explained - Blender 3D. - YouTube
Blender: Fixing a non-manifold mesh tutorial - Blenderheads - Mod DB
Non-Manifold Geometry: Your BIGGEST Issue when using Booleans (Blender Tutorial) - YouTube
Highlighting non-manifold edges - Blender 3D Printing by Example [Book]