I recently got hold of these photos from a mate of mine who builds these things over at a little company on the Northern Rivers, NSW. The company is called '6x6 AUSTRALIA'. They have a website and if you just Google their business name you'll find it online. It has all the info anyone needs to be assured it's THE safest way to tow just about anything around (without getting a proper Semi-trailer).
I'm saving up for one to build a Slide-on Camper on my Patrol wagon. That way I can still tow my Tinnie, and just slide the camper off at the campground to form a Base or HQ, and then still go down the beach or trail with the Tinnie, or out bush hunting. Other options for Caravanners is a 5th Wheler job, or even just tow your 25ft "Mobile Mansion" in safety and comfort, etc. The options are only limited by our imaginations but usually directed by whatever vision it is we see ourselves wanting to do while out there traveling.
Please let me know your thoughts because although I'm a little grey, I'm still young enough to not have much wisdom, and you "Old Greys" might actually teach me something yet. I aim to have the money for my 6x6 Slide-On Camper before the end of the year and you might just help guide my vision...
Not sure how much extra towing capacity, but I think they can set different utes up according to whatever the customer specifically needs their ute for. I vaguely remember my mate telling us boys one time how they just beef the Chassis reinforcing up and install heavier Springs and Suspension components for the ones that want to carry or tow more. Not sure, but I'll try and find out from my mate who works there.
I'll keep you all posted as I get closer to buying mine. I don't know enough yet, and that's the main reason I haven't purchased it yet as it is a significant purchase price for me as I'm not retired (yet).