I am trying to design a case for my raspberry pi and screen in blender to 3d print. I downloaded models for my raspberry pi and screen to use to make the case. I would like to use a difference boolean modifier or the bool tool addon. The boolean modifier says cannot execute boolean. When I try bool tool, I use difference and it acts like union instead. I have researched this and it seems to be a problem with the mesh I downloaded. I have tried remesh modifier, triangulate modifier, remove doubles, recalculate normals, pretty much all the suggestions. None worked. Is there something else that I can do.
These are the files I downloaded. I could not figure out how to add the files so here is the download link.