Thanks, I thought I should zip the tscn file, with all materials and textures and then load the zip file and then do
ProjectSettings.load_resource_pack("path to import.zip")
and I have all the assets in this zip file available as if they are in "res://", that is OK for me. didn't try it yet after exporting it as an application, but in Godot it seems to be working, the loading of the zip file.
Though you said if I have a project in "res://" Godot is importing it into .import as .scn, I placed a .tscn file in res:// and could not file any .scn file in .import. I thought I might be able to use .scn file instead of *.tscn, that is what you seem to be suggesting, but I could not find one.