Hi @geert_2 thanks for the great tips. I'll might have a look at DesignSpark but I'm using FreeCAD because it FOSS software/GNU, has many workbenches, and can be scripted with Python. Yes, it's been quite unstable, but I haven't had v0.18 crash on me yet.
I can hear from what you're saying that it's not so easy to click things together. I think I might be better going with a regular screw recessed into the bottom of the base and going into a nearly big enough hole in the bottom of the top section. I'll let you know how it goes (very slow spare time project).