Dont even know what our maximum is here. So I had a look on the net. (google is my friend).
Well that didnt help. Now Im totally confused. Not to sure if it is 3500kg or 4500kg. You might want to have a read through this
Caravaners Forum • View topic - Max towing capacity
have a look at the second link in the first post (the pdf file)

also this mob says its ok with a 9000kg GCM
5th Wheelers Australia. Small Fifth Wheelers for Australian Utes. - Tow Vehicle Guide for 5th Wheelers

so add em all up and divide by three and you might be close.