We went for 52 days in 2013 and loved it.
We rented an older Toyota HiAce-based campervan from Cruzy Campers, picking it up in Christchurch and returning it to Auckland. We spent most of our time on the South Island and in fact felt we could have used another week or two on the North Island. Looking back on it, we had a great introduction but, in truth, a superficial one. We'd typically spend only a few hours to a day in any one place and camped in a different place each night. We walked daily but did not hike any of New Zealand's famous trails or 'tracks' for more than a few hours at a time.
We used the
Official Camping New Zealand app to find camping and took advantage of freedom-camping spots whenever possible. You'd also want to read up on current policies on freedom-camping. It's important, for example, to understand that many freedom-camping spots are only open to vehicles displaying a sticker certifying that they're self-contained.
We rented a GPS from the van-provider but didn't like it. I had taken mine along as a backup and ended up buying the Garmin map card for Australia and New Zealand in Christchurch at a much more expensive price than I could have gotten it in the US.
One thing I wasn't fond of was the camping prices were charged on a per-person basis at many pay-camping sites. So you'd see a camping price advertised as $15 but it's actually $30 for a couple.
In general, prices seemed high. Fuel is of course high (currently > $5.50 a gallon) and diesel fuel was quite a lot cheaper. We nevertheless elected to take a gas-powered van because we preferred its layout. I remember being surprised how good the gas mileage was on the HiAce (more than 20 mpg, if I remember correctly).
Driving on the opposite side of the road and shifting the manual transmission with the left hand wasn't difficult to get used to but did require some mental adjustment, particularly where there are turning lanes.
Wi-fi availability was limited for much of our trip and we mostly had to pay for it, even in many coffee shops. We were nevertheless happy to find it at all-- we just had to limit how much we used it to the bare essentials and plan on having connections a few days apart.
For a phone, we had a prepaid el-cheapo phone included with the camper rental but had to go buy minutes at a local mall in Christchurch. And after the first night sleeping in the van we decided we needed to add a topper to the mattress.
