I have just finished fitting the suspension/steering hardware I mentioned here: http://www.theultralighthiker.com/twin-shock-absorbers/ I then loaded up the camper on the Defender. Let me say the difference is astonishing. The whole rig now handles like a passenger car; the ride is wonderful; everything feels so safe and relaxing. It is so easy to keep the steering on track on even the narrowest roads. Looking forward to many interesting trips. Watch this space!
This concludes the mods we needed to make the vehicle handle the (somewhat unbalanced) weight of the camper. I will also be fitting a second under tray 85 litre water tank, and switching out the hot water system for an instantaneous one which will save 30kg in overhang (and total) load, eg: http://greenrvproducts.com/girard-tankless-rv-water-heater/
Here are all the mods we needed (and advise): Move all possible weight to the front of the rear axles and below the tray (at least down and forward – this may require modification of the camper, or careful selection/design before purchase/build); standard height heavy duty springs and twin shock absorbers front and rear, heavy duty return to centre steering damper (described above); seriously upgraded shock absorbers; polyair (rear) assist suspension (inflate to max ie @ 35 PSI – NB also: tyre pressure needs to be vastly increased under heavy load. Recommendations are something like +5PSI per additional 100 kg! – tyres need to be ply-rated for such pressures. Check!); fit anti sway bars front and back; fit under tray storage boxes (4) and utilise storage behind seats; fit a winch and bull-bar to the front of the vehicle to help to balance the load (NB: the vehicle’s suspension has to be upgraded (or match) the total loaded vehicle weight plus eg a 10% ‘margin of error’ or it will never be safe – and might not be insured!)
NB: You will always have extreme difficulty making a dual cab (safely) carry a camper or other heavy load. Some are (much) worse than others, due to overhang, etc. Land Rover Defenders are complete stand outs in this category – as well as in genuine off-road (clearance, entry/exit angles, etc) & many other areas. It may just not be possible to fit a camper to your dual cab particularly if it has a tub. Professional advice should be sought. My experience is that like most other professional advice it is pretty hopeless though! Happy Camping!