Surfaces Won't Knit in Solidworks

I'm designing a part cooling fan duct for a 3d printer, and my process for designing ducts has generally been to model the airflow path as a solid body and then shell outward. Due to the complex, small geometries of this particular duct the shell outward command wouldn't work.

So, I offset the faces and then went about reconstructing the gaps between them with surface tools. However, when I try to knit together at the end, it won't knit, despite being constructed using edge relations. No gaps are detected outside the threshold of gap control in the knit function. Using heal edges doesn't seem to help. I know the model is very messy as this was my first time trying to use surface modeling tools and I wasn't very good at it, but I would like to get this to knit if possible.

For now, I've successfully created the file I need to print by exporting the surface bodies as one stl and re-meshing in blender, then using a boolean to subtract the air pathway, but I would like to have this model as a solid body so that i can integrate it with other parts of the 3d printer tool-head.

If you have any suggestions let me know, Thanks!