Righto all you engineering lot, towbar has been fitted with a ball rated at 3 tonnes
Question, 
now realise that all that could come over the 3 ton mark, originally designed to carry car and matierials to make my own diesel, then add Judys laundry my lapidary equipment plus rocks  ,  and you have a heavy trailer,
DO NOT WANT TO SELL MY PATROL, for a littler diesel, she's too bloody good, 
So thinking of A frameing the Patrol,
or building a lickle trailer with two wheels and put Patrols front wheels on it, bugger the laundry, and the manufacturing, and can carry the lapidary in the Patrol 
Judys Commodore will be sold so willbe reduced to one vehicle to rely on, and that is the Patrol, 
Any suggestion, serious stuff this , all smart alecks will be severly reprimanded
,no giggling, no rude stuff, so be nice
  
 

Bugger that puts me out .

no way mate, you can try, the same as everybody else, go on , you can do it , just think nice thoughts

So what is the problem with the patrol on a full trailer ?

See a lot of buses getting around on the east coast with a small suzzi behind on a two wheel trailer but a patrol is a big ask to drag around the east coast, on flat ground maybe . The A Frame could be you best bet It would take some complex calculation from an engineering perspective to get the two wheeler exactly right , maybe a suck it an see approach if you don't have an engineer on tap or a pocket full of dollars for one . Here in NSW the Fuzz will pull you over and ask to see the compliance plates and weigh bridge certificates if it even looks the slightest bit unusual. Don't need to draw the crabs they will find you soon enough

Might be a bit of an issue with the 3 Ton tow limit. 

My Patrol weighs 2.8 ton unladen according to the compliance plate.  Add to that the trailer of what ever sort  you choose & what you load in it & there might be a problem.

Way back in 2000 I watched a beautiful Winebago pull in to the top area at Broome's Cable Beach CP .. It was the same maroon & gold as my then newish Patrol .. so it caught my eye.  But lo & behold as it came around the corner, I saw that it  was pulling a tandem trailer with a  s t r e t c h e d  version of my patrol (same colour scheme) on top!   Bugger!


I did read somewhere about issues with 'A' frames compling with state laws, but as I was not particularly inetersted I didn't examine the details.  I do note however, like Wombat,  that most Motothomes so equipped pull medium sized RVs or smaller.

You don't want much do you? I like restoring old clocks ( must post re that) and there is no way I'd be allowed to take my teensy weensy NC machining centre with me.... SWMBO can take her sewing machine and that's OK.
Seroiusly I'd either a) leave the patrol at home, b) sell the Patrol and buy a compact soft roader  - Suzuki or something that size and tow it on an A frame. Have you checked on what you can legally tow? May be ok to have a 3000kg ball but there are restrictions on the overall length of rigs.
If it were me I'd be towing a smaller 4x4 to get of the beaten track with.

MIke
If I understand your question correctly, you wish to tow this trailer, but its gross weight is larger than the tow ball capacity.

Why not change from a ball to a pintle hooke? The ball capacity is just that, the rating of the shear force of the ball and tongue.

Obviously the tow bar will need to be checked for the greater weight, but normally this is not a problem. Also the trailer itself may need a higher spring rate, and a change to its compliance (which will be the deciding factor on this)

Obviously got more thinking to do, thanks a million for the comments, you have bought up a heap of things I hadnt thought about, or bought to the surface of the mind, just sitting simmering away waiting on answers, Some tough discisions to be made again thanks

to exceed the ball rating is sheer lunacy as is a small two wheeled trailer, the little trailer is designed primarily to haul front wheel drive vehicles and automatics around with the sole purpose of getting the "drive wheels" off the ground the two wheeled trailer itself is dead easy to construct and any bloke with a shed can do it providing he has a little knowledge in weight transference and access to an old truck, I would not drag the patrol around, the bus has enough on it's hands now without adding another three ton behind it, grab a little suzie (750 kgms) then drag it with an a frame or a purpose built trailer to hold the car, genny, washing machine extra water and whatever, all up probably under two tons Basil I love old ansonias and early english triple chime, I have three 1800's ansonias including "the royal" all in pristine condition, I have 4 triple chimes in the shed awaiting cabinet reconstruction (when I get the time) I am an avid collector of the old time pieces but am allowed only so many, I also have a very early black forest german cuckoo clock which I am not allowed to run