[JRTJH]

Something that hasn't been suggested is the consideration of what you're going to do with the truck and trailer after your "saga". If you plan on selling it at the end of your journey, then buy what you want and enjoy it. If you're planning to keep it in the US for future years, then consider it an investment and spend a little more on the things you believe you'll need.

If, however, you're planning to ship it to Australia when you've completed your journey, then you might want to touch base with someone at an RV import center there. Learn about the rules for importation, the restrictions (both legal and practical) with the specific rig you're considering. Things like converting the 110 VAC system to 220 VAC, how the appliances (air conditioners <two>) will interface with the different voltage systems, availability of parts to convert the trailer to meet Australian requirements. It may be (and then again, it may not be) that you can't import that particular model because of something as simple as it's 6" too long and not allowed.....

Without knowing your plans, this is not a "don't do it" but a "be sure you can do it" kind of suggestion.....