I haven't towed a caravan as such but towed a tandem trailer (1400kgs) with my race car in it for 40 years . Single axle set up wrongly will put a lot of load on the tow ball ,cause swaying and generally uncomfortable trip but some have no trouble at all .I built a trailer for a mate to tow his car with single axle and was OKish but later when we extended the trailer by 600mm and put another axle under , it was a totally different thing to tow , more stable much better ride in the tow vehicle. Also depends on rocker type load bearing springs or slipper.