Single wheel bike trailers are great for off road or long distance touring. These have to have a 5 mm quick release skewer to attach onto the bike. They have a deck which you can strap a pack or dry bag onto. My design is about 1kg lighter than a BOB trailer.
Hire a single wheel a trailer for your tour of the South Island for $100 a month or buy one for $300 and I can buy it back from you (typically $150 in reasonable condition). Courier back to Christchurch can be arranged for $50 as long as your last accommodation is ok having the pickup from their place.