GH Creating one Solid (solid union and boolean union don't work)

Hello everyone,

I’m working on an assignment for university. My model is done, but it has to become one closed solid (it has to be able to be 3D printed) In grasshopper solid union doesn’t work. And in rhino itself it’s not possible to use boolean union to join all the closed polysurfaces. It keeps failing primarily when I try to join two polysurfaces above each other. Does anyone know how I could fix this? It should have no manifold edges etc.

Thank you in advance!
3Dprint.3dm (6.4 MB) (25.5 KB)

[Edit] Sorry! I’ve added a cleaner .gh file. hopefully it makes everything a little clearer

this might be a solution:

note, it tells the brep is open: after baking the whole thing just explode and join everything (18.4 KB)