Hi Jason_77
there are loads of companies you can rent camper vans with. Maui
http://www.maui.co.nz/ do mostly new campervans.Then when these get a bit older, they are rented out under the Britz
http://www.britz.com/ label. Then when the Britz vans get older again, they are rented under the Backpacker label. It depends on what your budget is. We went with Britz and the van was in good condition. A few creaks but nothing out of the ordinary. Saw a LOT of Kea
http://www.keacampers.com/ campervans over there but didnt know about these before we left so dont know what the prices were like.
http://www.maui.co.nz/
http://www.britz.com/
http://www.keacampers.com/
We rented a long wheel base campervan with shower/toilet facilities so we didnt need the shower facilities in the campsites we used. My hubby is 6ft 2in and laughed when he saw the shower but he was a convert by the end of the hol. It did what is said on the tin!!
As far as camping was concerned, we mainly stayed in the DOC (Department of Conservation) camp sites that cost a pittance. Most of them had cooking/shower facilities but very few had power. So about once in every three days we stayed in a serviced site to charge up the mobile phone etc.
http://www.doc.govt.nz/templates/summary.aspx?id=37254
[broken link removed]
On the last night we stayed in Akaroa Top10 park and the view was SPECTACULAR. If you go out to Banks Peninsula, call in to the park early, take a drive around and see if any of the really nice sites are available, and book asap. I think you can actually book accommodation over the phone if you are sure of your dates but we were just taking each day as it came and were just lucky to get one of the best spots. They go quickly. (Theres a nice winery in this area for a liquid lunch too by the way..!)
On the west coast especially, there are some really ice places where you can just pull off the main highway and camp for the night. As long as you are out of general sight the locals dont seem to mind. And the DOC have a list of sites where you can dump water, toilet etc and fill up with water without having to call into a serviced site.
lastly, i didnt find the distances too vast. The longest drive was to Milford Sounds but its such a nice trip that you dont mind the distances.
If i think of any other tips. I'll pass them on or if there's anything in particular you'd like to know, let me know.
Hope this is of help,
Emmt