it is also illegal to tow a vehicle on anything other than a rigid bar in SA.
Not sure that the law is quite that explicit.
From the current South Australian regulations:
AUSTRALIAN ROAD RULES - REG 295
295—Motor vehicle towing another vehicle with a towline
(1) The driver of a motor vehicle towing another vehicle using a chain, rope, fabric, strap or wire (the "towline") must comply with this rule.
Offence provision.
Note—
"Motor vehicle" is defined in the dictionary, and "vehicle" is defined in rule 15.
(2) If neither of the vehicles is a motor bike, the driver must keep a distance of not over 4 metres between the vehicles.
Note—
"Motor bike" is defined in the dictionary.
(3) If at least 1 of the vehicles is a motor bike, the driver must keep a distance of not over 2.5 metres between the vehicles.
(4) If the towline is longer than 2 metres, the driver must attach a white or brightly coloured flag, piece of cloth or other similar material (the "warning material") to the towline in accordance with subrule (5).
(5) The warning material must:
(a) be substantially square or rectangular with 2 adjacent sides at least 300 millimetres long; and
(b) be attached midway along the towline; and
(c) be visible for at least 100 metres from either side of the warning material.
(6) Subrule (2), (3) or (4) does not apply to a driver if the driver is exempt from the subrule under another law of this jurisdiction and is complying with the conditions (if any) of the exemption.