3D Selection Modes

[[Bl...]]

Is there a way to select a patch, then select everything that is inside the patch?  I have to separate a single mesh that has 3 parts into 3 separate .stl files to prepare them to put in an inspection template project, as well as cleaning up small bits of material from the fixture.  I initially was using select through surface, then I discovered that select patch was much faster.  However, this morning I realized that there are components inside the part (Hollow areas that don't touch surface) that would also get deleted from the new exported mesh.  Is there a way to select everything inside this patch?  Or use the outside surface of this patch as a boundary for selection?

I am currently using Blade Inspect Pro 2022.