4 weeks to do the whole of NZ? Whistle stop tour or what!
Well, maybe as a route (although I dont know all the roads) you should head north first, take in a bit of north shore and northland. I doubt you'll have time to do the whole of Northland, so you'll have to cut it short!
After that, swing on round to the Coromandel for a nice scenic drive. Some lovely spots up that way, although dont fall in love as the houses there cost squillions!
After Coromandel, head down to Tauranga/Mount.
Next across to Hamilton
Best part of the whole tour
After that, you can cut down to Rototua, and on to Taupo.
From Taupo, head across to the eastern BOP to places like Whakatane, then do the Gisbourne, Hawkes Bay, Napier bit.
From there, you can either go down to Welly through Woodville etc, or cut across and have a squizz at Palmerston North before going down. You'll miss New Plymouth with this route, but I reckon that would be a hard journey in a camper anyway.
From Welly, hop on the interislander, and in to Picton.
After that, you're on your own! Never been to the south island