I can only relate to portable units sold in the UK. That means their usually designed for domestic use, rather than caravan, and are not set up for the extreems you might find in Aussie. As I'm sure you know, to make AC work most efficiently, you need to prevent any unnecessary air exchange between the inside cooled space and outside. This is why the better systems are usually are split, and use a small bore connection system, or their condenser and evaporator systems are properly segregated internally and their respective inlets and outlets are designed to maintain the segregation and may use ducting for the air circuits.
The systems that are designed specifically for recreational vehicles, do mange the air circuits, but they are not classed as portable, being fitted into the caravans, what we see as portable "AC" units are usually stand alone devices that either use evaporative cooling using water(otherwise humidifiers, and are less effective) or devices that use a compressor refrigeration system but usually only duct the condenser (heated) air away, meaning it uses some of the internal air to carry the heat away, but that means the room has to allow more external air in to replace it. That significantly reduces the efficiency. You also have to manage the exhaust duct, which either means having a window or door open, or to have hole cut for it somewhere.
The next concern is the expectation of performance, Again in the UK and EU, the amount of mains (230V AC) power into a caravan is limited anything between 3 to 16 Amps, and that means the cooling capability of the units is nothing like the performance of a cars AC.
If you have better power options, then you should investigate products available in the USA, where I believe some RV's will have AC systems rated up to 7kw!