Mrs Guava and me had idea to do this campervan trip two years ago, but found no availability at reasonable price. So we took our tent and this was was nicely cleaned and fumigated by Auckland customs. We rented a saloon car for one month from Auckland , drove to the airport hypermarket where we picked up discount camping equipment , cold box , etc and “did” pretty much all of North Island. We pitched our tent in motorcamps using the tactically placed car to block other vehicles from inadvertently running over our tent in the night.We met interesting people while cooking in the motorcamp cookhouses. We drove a long way and the speed and gas mileage of the car was far better than that of a camper van.
Had a great time at reasonable cost in an expensive country.
I Just thought I would mention this for consideration as a good alternative to the campervan idea.