When I drive solo, the vehicle is perfect, but as soon as I load the rear with camping equipment (chairs etc - not too heavy?) and hook up the caravan (±110 kg towball weight), the rear sags pretty much to such an extent that the headlights on dim actually blinds oncoming traffic!! Brights can be used to hunt Giraffe!!!!

Is there any adjustment that can be made to give more spring resistance in the rear without going for upgrades etc and not resulting in too hard a solo ride??

If so please advise me on a reliable and trustworthy supplier of such adjustment service in the Pretoria area.
Thanks in advance.