Hi Tracey
We travelled part of NZ by Campervan in the summer but I do know some people do it in Winter, as the Campervans are especially equipped and insulated for the weather. I include a link of FAQ that also answers questions regarding the need for snowchains in Winter etc. I cannot help with accommodation along the way, maybe you could enquire from the link. Hope this helps.

Campervan New Zealand Frequently asked hire questions