There is a lot of media interest in the legality of many caravans on the roads at present. Police and State roads authorities are also doing random educational road side weight checks.
A recent voluntary weigh-in in Brisbane found 58% of vans weighed were overweight and therefore unroadworthy. I can assume that these would not have all been fully packed for holidays.

After the double fatality in NSW early 2019, I believe it will become a topic of enforcement in the very near future.
It is therefore vitally important that when buying a new caravan that you check the tow vehicle and caravans load carrying capacity and expected tow ball weight when loaded prior to purchase.
It is recommended to have a tow ball weight of approx 10 - 12 % of the ATM (Loaded weight) for most common size vans on the roads in Australia.
Remember it can be very expensive reselling your van and buying a new one that is legal to tow with all your usual items and accessories on board once enforcement is increased.

If you are one that carries a lot of personal items, have extra van accessories and do a lot of free camping (batteries, water etc). you will need a large load carrying capacity.

ATM minus tare gives you load capacity.

600kg plus is common and currently suits most caravanners. Below that and you may need to have a close look at what you carry.
Remember water, mattress, gas are all load as well.

FOR EXAMPLE - My wife and I are currently looking at purchasing a new caravan and have looked at many brands and models. We need free camping ability and some space to live in for a couple of years on the road.

Jenny and I have found the Coromal EV632S / RTV seems to best suit our individual needs and future plans.
At around $73,000 RRP. we believe it also represents great value for money and is on special at present making it even cheaper. (Nov '19). 

I will add some extra solar and battery capacity and a grey water tank as personal preference.
The tow ball weight is 190 kg at tare of 2,235 kg and has an ATM of 2,885 kg. Therefore load carrying capacity of 650 kg.

This also gives this van a tow ball weight of approx 8.5% at tare or when unloaded.
The Coromal vans have a generous front boot plus this model has a compartment on the A frame for 2 x gas bottles and extra storage for what ever you may want to put in there.
The 8.5% tow ball weight at tare allows for us to put some load in the front boot and A frame storage which will add extra weight onto the tow ball.
s long as we are sensible and don't load it with concrete blocks we should end up with around the 10 to 12 % tow ball weight which is the industry safe towing recommendation for that size van.
If you choose a van without a front boot you will have to do different calculations for the above.

As I will be also upgrading my 2013 BT50 dual cab tow vehicle to an Iveco Daily dual cab with the 205 hp motor, huge load carrying capacity, & gross combined weight and the 3,500 kg towing ability it is well within the the capabilities of the Daily. 

Hope this helps in what to look for in buying a new van and not just the large screen TV or other heavy luxury items designed to 'sell'.
Do your homework first.

If it is not going to be legal to tow it is a big cost item to have just sitting in the yard.

Stay safe