you mentioned no APU, so how do they handle the loading? External APU? Never done freighters in my life, so really have no clue. But is it common practice for freighters to remove APUs to increase payload?
I've seen some SQ Cargo 742Fs never tried to check if they had the APU or not.
The ATP has no APU hence uses GPU after Engine Shutdown.The Starters are Electrically operated & not Pneumatically driven.More Advanced Aircraft have APUs installed.