baby dolphin fat is good stuff, will prevent chafing no problems. Hard to track down but you are in NZ so just ask around
ok, chafing is a fairly common issue in triathlons, so there are some home made recipies and some commercial products favoured by those guys; if you want to do some research have a look at tri forums.
Home made is mostly lanolin (sheep fat). Assuming there arent too many sharks around (and notice I avoided NZ and sheep jokes...). Some make up a mix of lanolin and vaseline but petroleum based products are highly unrecommended as jaffa said. So you can try lanolin
Commercial products include bag balm (which is mostly lanolin anyway), bodyglide, triglide and a few others. Triglide seems to get the best reviews (search 'tri glide anti chafe' or you will end up with a lot of motorcycles)
A simpler option (and my suggestion) is a short sleeve high neck rash vest worn under the wetsuit. Might look a bit weird but whatever. Or maybe a 'skins' style compression shirt, which might fit a bit better under the wetsuit. No need for a thermal vest.
eg
http://www.surfdome.com/billabong_rash_ ... ack-124077