Another option would to be having two plugs-one for the 240V 30 amp and the other for the 120V, Raychem (amongst others) make "Y" heatshrink boots for splitting cables. This method will be easier as it will allow the use of standard plugs for the services rather than specialised connectors. Problem is the strain on the "Y" junction due to strain may cause more grief than good.
I had a look in Australia for you, I found an IP66 rated connector which had 7 pins but only good for 20 amps.
