About 5 years back we did 3 weeks in NZ North island around April time. Camper van hire was cheap as chips with Maui so we went for a massive 6 birth van. We both absolutely loved it and camper sites were super cheap as well. We miked it up with staying in a couple of nice hotels at the start and finish of the holiday as I think it was only about £45 a day for Camper van hire. If you do go to NZ then you must hire one of the GPS tour guides devices. They totally make the holiday as they tell you all about the history and culture as you drive as well as pointing out what is around you.
Driving in NZ is really easy as the roads are just so quiet