Creating a rib structure from a negative solid or brep

Hello!

I'm fairly new to grasshopper and my ultimate goal is to create a rib structure from a pipe-extruded solid.

So this is how I am going about the logic. I created a closed curve and piped it to give it thickness, then I created a solid box around this piped loop leaving parts of the curve outside the box intentionally. Now I am trying to subtract or carve out the path of this pipe from the box so as to create a tunnel into this box with an entrance and exit, but I can't seem to figure out how to do this.

Then I want to convert this subtracted solid into a stack of horizontal planes where I can manipulate the space between the planes, and then finally brace them together by vertical ribs on the edges.

I highly appreciate any help. Attached are the files to where I got to.

Thanks