from auckland to uk via c america

Hi, I'm a UK chick, living in auckland and have bought a camper van here as there are lots of decent cheap vehicles. I've come up with a plan to drive my van back to the uk by having it shipped to Nicaragua and driving through central and north america and then shippung it from the east coast. Is this crazy? I am open to the idea of buying or hiring a van in Nicaragua to do the same trip if it will be much cheaper but am concerned about leaving a van in the US and how customs etc would work. I think the US embassy website says that as a foreign international using a vehicle for personal us, I wouldnt need to pay but find this hard to believe.
Any suggestions of how I start looking at the kind of paperwork I would need to do this and cheap shipping methods, it can be super slow if that is cheaper.
Thanks, loving the website, so much information but a bit overwhelmed at how to start - got the van though!
Kate