Best semi-permanent method to Travel Australia?

I'm planning in about 4 to 6 months time (depending on finances) on traveling this great country of ours at my own pace.

I'm a budding photographer and due to a recent marriage break up I'm intending on going walkabout on my own. I will be sightseeing and documenting my travels via video and photographs.

However, I'm at a bit of a cross road in regards to what method would be the best way to do it. Do I take
a campervan-sized motorhome, a small bus like a Toyota Coaster, or a 4WD towing a small off-road caravan?

It will just be myself travelling.

I wish to see or visit the sights that the everyday Joe Bloe doesn't often see, hence I'm thinking a 4WD would suffice but I'm not 100% keen on towing a caravan or sleeping in a rooftop tent on the side of the road. With the caravan I'd obviously have to unhitch whilst I took the 4WD bush, as I'm sure I'd have some difficulty taking it up some 4WD tracks to get to that stunning view in the mountains.

My concern is that this could possibly be a long term living arrangement as well and also I have security concerns in regards to my camera equipment and computers that I'm planning on taking with me.

So in this respect I guess I small motorhome would do, but a bus converted to a motorhome (perhaps even towing a small 4WD) could be the go. Even a small secure caravan would do where they would give some amount of security against theft.

But I'll be on a fairly small budget which I will also have to live off while I travel this great land (unless I can find work along the way). I can't afford anything too extravagant.

Basically I'm planning on living in it as well as travelling.

So I'm looking at something that offers the following...

· My main concern is security.
· Flexibility to go off road if needed.
· Sizeable for long term living (single).
· Economical fuel-wise and also easy to get parts for in the outback if needed.
· Self-sufficient as in solar power, etc.

I'm after some advice from anyone to help me decide the best way to travel. After my divorce I'm not sure how much exactly I'll be left with after I pay my debts. But I'm hoping to spend no more than $15,000 to $20,000 on the vehicle and or towed caravan.

Thanks for your time and again all the best for the New Year! :)

Alex, Vic