You're right to be concerned. Polymer clay begins curing at a relatively low temp, and though it can be reconditioned even if it's been cured, I hear (by grinding, soaking with Diluent/etc, then lots and lots of kneading/etc), it's hardly worth the trouble.
Your boat to Thailand might get quite hot depending on the season (August would be pretty bad and it doesn't take long to cure the clay, but don't know what route the boat would take getting there, etc), and the company may or may not have provisions for keeping things being shipped within a reasonable temperature range (no problem if polymer clay gets really cold btw), etc.
Your container of clay could also be affected by just where it is on the boat, and whether it's close to engines, etc.
What I'd do is see if I could find out:
...if there's any environmental control for the shipping area at all, and what that range would be
...if there is any environmentally controlled area on the ship they'd allow you to store your clay-box in for the trip
...if the shipping company knows anything about how people deal with things like this when shipping with their company or others (someone reliable since you'd be placing your
bet on their advice)
If you do just have to ship it in the 40' container, that's pretty large so there would be a lot of room for "insulation" protection. I'd wrap the clay (individually, laid side by side into larger "bricks," and/or altogether in it's clay box) with a lot of clothing around it or other things* that would be good insulators, then place it in the very center
of the 40' box. That should keep the heat from reaching it as much as possible, and even if it did get some heat it would be most likely to be on the outer areas of the clay or box (clay is dense and insulating too) so put your least favorite or cheapest clay on the outside
Oh, and I don't know this for sure, but I'd probably keep all metal or ceramic items or tools (pasta machine, etc.) in another area of the shipping box since they could heat up more easily and transfer heat if near the clay.
*maybe even insulation material of some kind from the home improvement store, or perhaps wrapping with certain other things that are highly insulating (those emergency silver-backed blankets?, etc.)
I don't know how long you'll be there or how much time you'll have for clay, etc., but just figure out how much it would cost to replace all the clay you might lose vs. how much it would cost to order more from Singapore, Australia, etc., while you're there and let that help you decide.
You might also decide to pursue another type of clay while you're there (some form of air-dry clay probably that you could buy, or could make at home like bread clay or salt dough or even pulp mache, etc), or just get into a whole new craft/art that's available there.
(Btw, if any canes
were to get cured you could still use them in some ways by rewarming then cutting slices--thin, thick or even long--with a long blade; holes, if necessary, could be drilled or hot-pin-tipped, etc., carefully. The slices could be used as is, or perhaps by pressing into raw clay, or by making a clay or other-material frame around the slice, or by putting the slice on a backing piece of clay or on something else, etc...some consolation anyway.)
P.S. If you end up leaving your clay at home be sure and store it well too, especially if you'll be gone a really long time --inside closed Rubbermaid containers or wrapped in aluminum foil*/etc, dark, and cool would be the absolute best, but less protection should be fine too as long as there's never too much
heat or UV light.
*canes or slices/etc. aren't best with foil though since it can leave dents in the clay--wrap those with baggies around and around, etc....and don't use waxed paper since it's slightly porous and will eventually leach plasticizer from the clay