Organic STL Mesh to Surface

Hey Guys, I’m really stuck on this on. I’m trying to take two scans, provided as .STL, and do an offset and extrusion down for milling for molds.

I managed to nail it on the first scan sample using planes through mesh to create curves in order to loft a surface I could work with, but it does not work with the other provided samples - at all.

Heres a video of the intended output as it worked on the first sample:

Here is the script as it stands with both sample meshes included, upper and lower sections… I think I need a better way of working with the meshes, but I have tried everything that I can think of to no success. (2.4 MB)