I just got some random ideas for RP cargo today and now i found this thread so if it's not a problem i write down my ideas here, they are something similar to your PMH.
Medicalbay: this can be used on ships RP'd as Mediships.
Engineeringbay: maybe it can be a junker stuff for repairing salvaged things or to build stuff up from the scrapmetal.
Dininghall: this one is for Luxury Liners to feed your VIP's
Prisoncells: for Prison Liners and Capships.
Weaponstorage: for militaryships
they can be attachable parts like the armorupgrades