Bay of Islands and the far North.
This trip has many stops at great locations, you could travel this distance in as little as 3 days but to get the full enjoyment I would recommend at least 7 days.
Itinerary
Matakana Market, this is a great place to stop to purchase some food for your trip.
Tawharanui has a great camping site run by the Auckland Council.
This beach is very private and a great place to spend a few days.
Goat Island, this is a marine reserve which means you are guaranteed to see at lot of fish when you go snorkling.
Matapouri, if you have time spend a few days here and see if you can find the mermaid pool, it is worth the effort. 
Matapouri again
Bay of Islands
Cape Reinga Top of the North Island

The very tip of the North Island
Light house is still operational
90 Mile Beach, do not take your Campervan along this beach is it will not be covered by insurance

Rarawa Beach
Rarawa Beach
Rarawa Beach Camp Ground
Henderson Bay, very beautiful 
Henderson Bay
Henderson Bay
Kawakawa here the world famous artist, the late Frederick Hundertwasser, has made this town a must stop 
Waipoua Forest and one of the largest kauri trees
Kai Iwi Lakes - They are world famous and crystal clear
Langs Beach
Langs Beach
Langs Beach
Mangawhai 
Parakai Springs Hot Pools, relax and unwind. Or you could jump on the slides and have some fun.