As far as I'm aware, 50% of the vehicle must be devoted to accommodation on a permanent basis. This kinda prevents horse trucks putting in sink in one corner and laying the bed down after the horses have been taken out.
In 2004 when I did my bus there was an advantage in being tegistered as a M/home in that the annul registration was cheaper. I don't know if that is still the case.
Another advantage was that you didn't have to have a TSL or Transport Service License, you also were absolved from having to use a Work Time Log Book although you still had to act within the law.
Now all that applies to vehicle for which a Class 2 or higher drivers license is required. For your vehicle the above may not stand.
I would get discussing this with NZTA or a VTNZ inspector.
Duct tape is like "the Force", it has a dark side, it has a light side and it holds the universe together. nothing screams poor workmanship more than wrinkles in Duct tape.