I wonder about getting a trailer custom made so it can have the door on the driver's side, and be able to be rewired for 220 with ease once back in OZ, perhaps with conduit for all 120VAC wires so they can be easily replaced if necessary. Plus, with it being custom made, the door can be on the UK side, as opposed to the continental curb side. This way, it will not be awkward to use on the left-hand driving roads when back.
I don't know any custom travel trailer makers, but horse trailer companies can do this. For toy haulers, DuneSport has been mentioned.