The import function just calls the native Sketchup importer and does some clean up, of that ignores some properties than there is no way for me to figure out what they should have been. But if the native importer DOES import them properly than I should be able to fix it, but I'm afraid that's not the case
I testet it. And the native importer does export and import the Longname. Please find attached the file and a screenshot. I modeled a space, put the Longname attribute, exporter and importer again.
The import function just calls the native Sketchup importer and does some clean up, of that ignores some properties than there is no way for me to figure out what they should have been. But if the native importer DOES import them properly than I should be able to fix it, but I'm afraid that's not the case