Not being a common size you MAY have difficulties if you need repairs. Our convoy (not our car, LOL) needed repairs in both Bamaga and Weipa and found them really helpful. But it was vehicle repairs, not trailer parts. Weipa is bigger, better equipped, and probably more likely to have the parts you'd need IF anyone up that way was going to have them, I'd say...
One of the cars in our convoy bent a tyre rod (which could have been avoided, but such is life), the other needed a set of bushes replaced (that perhaps should have been done before we left!). Have your vehicle and trailer in the best possible condition mechanically before you head off. The corrugations can be brutal. We had a leak in our rear diff (fixed by tightening only, bonus) from the PDR corrugations - the diff gasket managed to work its way loose! Check over everything regularly and hopefully you'll catch any issues before they become big problems.
Plenty of people tow up the Cape, but plenty of people also manage to write off their cars and/or trailers on the roads up there. If you're sensible about things you should have a fantastic trip with minimal to no damage. But things can always go pear shaped when you least expect it!
Agree with the comments about spare parts becoming a liability - you can't predict everything that could go wrong, and you can't take everything!
Consider taking a spare air filter for your vehicle if you haven't already packed one - light and doesn't take up much space. Travelling in convoy we really needed it, even with a good pre-cleaner and trying to keep a good distance from the car in front.
