TripleBee
Just look at your California from the side. You will see that the rear end is lower than the front end. This is caused by the 600 kg load you have as standard over an empty Transporter.X4 tyres both rears had gone down to the canvas on the very inner edge, rest of the tyres had miles to go!! Odd fronts due to puncture on motorway 18mths ago and the original front was pretty close to the wear bars so decided all 4. Not sure why the rear had gone on the inner edges dealer/tyre fitter said it possible due to having 18inch wheels, not sure on that but all 3 original Hancocks have covered 21,000 mls
This causes the rear wheels to be at an angle (top inwards, bottom outwards) making the inner side of the tyres wearing faster than the rest of the tyre.
This is negative camber, and can not be adjusted. The only way would be to fit stiffer springs at the back, lifting the backside up about 3 cm.