I can reliably inform you that B1900's in NZ are not certified for single pilot operations, private or ATO's.
Without the same certainty of reliabilty I think that Vincents B1900C has the standard Coat Locker/Hold configuration behind the Co's seat, opposite the Main Cabin door, with the 19th seat installed at the back of the cabin as part of a 3 seat row 10.
Air NZ/Eagle's B1900D's have no Coat Locker/Hold and instead have the 19th seat installed in it's place as Seat 1F which has headseat jack points for observers if required.
I doubt very much that monkeybdg's dad sat in the cockpit on a NZ ATO flight operated by Vincent Aviation on behalf of Air NZ.
Vincent is a Charter operator who maintain their business operating B1900C/D's and a DH-8-100 for overflow or engineering cover for whomever (plus Flight Calibration for Airways Corp using their C406's & a bit of Cook Strait freight) but they have contracts in place with Eagle Air for the B1900's to operate scheduled services on a regular basis. They have for the last 18mths been operating 2 BHE-CHC returns for Eagle, who are now about to purchase their 17th B1900D from the USA to replace Vincents as it has proved a sustainable service. Vincents are to be used instead on developing new Eagle routes involving HLZ-NSN, NSN - PMR, NSN - WLG and taking on the exisiting midday flight WLG-TIU -WLG for atleast the next 4mths.
S2K