Change all hidden faces to caulk

[mfn]

Main question: can we find out which faces are actually hidden?

[AEonZR]

Actually that would not only be the "covered" faces but all those directly connected to the void.

Since even bobtoolz did not integrate this, it should be fairly complicated. You would have to find brush faces that share the same plane, and more or less same location... to then find out if one actually covering the over due to a larger face size.

It might be relatively simple to check for brushes that share the exact same face. Though again special cases would need to be looked into: Like for windows in a wooden frame, here caulk would be wrong and nodraw more appropriate...