I've done this twice, once each way ! but to Canada.
A container is the only realistic option, otherwise your special load will need to have lifting points provided, Centre of Gravity, mass etc all marked clearly. It will also be limited to ships that take these loads, and not just container ships. I have watched some of the offloading techniques for these loads, and wouldn't want anything I owned to go through it. My thought would be to sell the trailer, there are probably difficulties in using in Auz anyway, and just get four wheels on your car, worse case is dollies.
Best bet it to pack everything yourself into boxes, and make sure this is really well done as they are going a long way, and then get a shipping company to give you a quote to load it into the container and ship it for you. If it is mostly in boxes it is easier for them to estimate volume. You will need a shipping carnet (The name may have changed now) so every box has to have a number and be on the carnet which your agent will need. We ended up bringing a car back from Canada and they simply drove it into the container (although you have to sign a waiver to say you have driven the car until it stopped because it ran out of fuel), and then nailed chocks around the wheels, front, back and sides, and then some straps through the car before closing the doors. The shipping company also are very good as guessing capacity of container. On the way to Canada they estimated a 20', and there was no more than 1' empty at the end. Your goods should not be simply continuously filled, they need restraint straps every so often to stop them starting to slosh back and forth. The very end should have a wooden wall built and nailed in, strapped in, etc so that when you open the doors there is not an outpouring of your worldy goods
The problem with used containers it that they are that, and may not be watertight. Our shipper coming back ensured we had a brand new container, and went in and closed the doors to ensure it was light tight, and hopefully water as well. You need to get below decks storage for two reasons. Firstly in high seas it is drier, and secondly if the weather gets bad and the ship into difficulties they will jettison containers to save the ship, and they can't jettison yours if it is below decks.
When I said drive the car into the container, that isn't entirely correct. The container arrives on a trailer, and stays there. So they arrange the removal truck behind it, both with their doors open, and then walk up a ramp through the side of the removal truck, and then across into the container. For the car they drive it up ramps in the removal truck, and put the ramps across to the container and drive it across. I did this bit and you definetely need to trust the guy giving directions.
Garden equipment needs steam cleaning, and I would imagine so will your car. They will check and are very picky.
Anyway, probably more than you were thinking of. If you want any advice about changing country just ask. Just remember to stay longer than a friend who emmigrated. They got off the plane in Sydney, decided they didn't like Auz and booked a flight back the next day. Total stay 3 days.
