Clive, I'm no snowflake boet, I welcome any input.
The 5 issues to had to solve:
To limit rear overhang on box.
How to get motorbike in/out the garage. (150kg)
How to get spare tyres on/off rear door.(100kg each)
How to lift garage door with weight of tyres. (300kg)
How to seal the rear door from dust.
I didn't want the bike and tyres stored on a platform outside on a chassis-mounted hydraulic lift.(overhang)
So a slide out drop down as per video, addresses all of these. The weight of a ram, pivoting hydraulic lift, is circa 500kg and doesn't solve the issues above.
The total weight of the current design including all the hydraulics and rams is ~600kg. So very little in the overall weight, compared to the pivot chassis system. The problem is not the mechanism, as any mechanism would have added 500+kg. It was the decision to carry a motorbike on the truck. That one decision has created an extra 750kg payload.
I don't have a problem with weight limit, as the truck's GVM is 18,000kg. All up, I'm now close to 11.5t.
If you've got a design that can accomplish all that then I'd be delighted to hear.