Mercedes Sprinter vans are since decades a popular choice to use as a base vehicle to turn into a Campervan or Motorhome. A large variety of models is around, whether you looking for a used or brand new van. The 4x4 Sprinters are most likely "the way to go" if you are planning to travel off grid to explore the more remote areas in Australia.
Particular the MWB models are a good choice, as they are not too large and easier to manoeuvrer and still giving you plenty cargo space to convert into a fully equipped RV.
Many ex Ambulance vehicles being used for DIY and professional camper conversions.
The Mercedes Vito is a smaller, compact van which thanks to his comfort to drive everyday and low total height can be the vehicle of choice- especially if you need a total height below the 2m mark.