Hello,
Welcome to the forum! Hope you get all your flights etc sorted out. Unfortunately I've only flown with Malaysian Airlines so cant comment on Thai.
Just a wee word of advice on the Motorhome thing. Not sure how long you will be staying in NZ for when you visit but seeing it by Motorhome can be a slower way to do things as the roads here are quite hilly and windy and I know just driving them by car can be a bit of a nightmare and I know from what others have told me doing it by Motorhome can be even slower.
It sure will be a good laff tho and means all your accomodation and travel are all paid for. What I'd say is try and plan where you want to go and add a couple of extra hours on just incase. Or even do part of your trip by motorhome and part by car??
I'm sure what ever you do you'll love your time across here
