To get from the South Island to the North Island you have to take a ferry to get there. It takes about Three hours to get across and it actually is quite the trip. Not only do you get to see Picton from a distance you also get to see Wellington before you have to drive through it. They also provide a service where you can take your car, van or truck over on the ferry itself. The whole process though takes a few hours and you end up sitting in your vehicle for a while before they let your lane go on the ferry itself. You start off with driving to the booth, the lady hands you a ticket, gives directions about the LPG tank if you have one and then tells you which number lane your in. The lanes go from 1-9 and you just drive up to the end of the lane and then turn off your vehicle and wait. 

Really the whole process is quite boring. You wait for a while. Other people are waiting. your wondering when its your turn and you just kind of sit and look around. If you have a book its a good time to read it and just relax. Once its your turn your directed onto the ferry and once you are at the back of a line you park, get the stuff you want and leave your vehicle and head inside. Once your inside you head up to the 7th or 8th floor and you get to hangout and have coffee, wine, beer, or food. They have free wifi and all kinds of areas where you can plug in your electronics and relax. They also have an open deck where you can go outside and observe your surroundings. 

Really the whole process was quite boring but its nice to have some time to chill and not have to go anywhere or do anything. The entire time I was on the ferry I was relaxing, drinking some coffee and water and all the while I got some work done and read my book. It was quite wonderful. Of course I also snapped a picture of Picton while we were leaving port. 

So if your looking for a connection, with your camper van, and want to do both islands you totally can. I highly recommend Intersteller. Clean, nice, and they can cater to your needs.