Making voids in a solid

Hi guys,

hopefully not bothering you with stupid questions. Anyways, I'm trying for two hours now to create voids in a solid. I've got a waffle model of a bookshelf (currently not exactly to scale in my script) and I want the entire waffle model to be held by a 4mm MDF. For that reason I decided to make voids for either the x-direction sections or the y-direction sections, that doesn't really matter to me. My idea is to offset the curve a bit inwards so that the 4mm MDF won't be cut all the way through. This is my aim. However, I did it here with Rhino and not with Grasshopper.

I've tried few approaches:

1) Deconstructing the brep which holds the y-sections and trying to extract only the bottom surface which I would then extrude 4mm in minus Z direction. Finally I'd use boolean difference between the 4mm MDF holder and the sections.

2) Move the surface a bit upwards in Z direction, so that it intersects properly the sections. Intersect sections with the given surface. Take the intersections, project them onto the 4mm MDF holder and somehow make voids.

Interestingly enough I couldn't cope with either of them. Hope someone would find a solution to my problem.

I try to keep my code tidy but please keep in mind that since I'm a newbie it might be slow and irrational.

P.S. I highlighted the MDF holder and the sections with light green in the Grasshopper file.