Sorry mate, I dont live in Sydney, but do have one of Aussie Jays. I have been very happy. probably spent clsoe to 100 nights over two years, and towed it close to 20,000k.
As far as quality finish and robust construction goes you wont fault them. Jason is a very down to earth guy, and as a qualified boiler maker his welds are spot on. in the end for me it was meeting him and having a chat that sold me.
AS has been suggested above, I'd rent a couple of different campers and go from there. Thats certainly what i did, I would have loved to have had 20k to spend but my budget was 10k, since then over time ive added power, and things like that.
As far as towing campers on extreme off road conditions, its not easy. To drive difficult terrain while towing, you need a very capable vehicle, and to be a very skilled driver. I wont get into departure angles, clearance and torque. If I want to access difficult areas I go with swags.
AS far as second hand units go, I spent about 9 months searching and veiwing them. My veiw differs from many on here, I think 2nd hand campers in good condition hold their value so well, I just couldnt see the saving. but thats just my veiw.
If youve got the time and skills you might be able to pick up a project camper and get it up to scratch.