See www.caravanworld.com.au/features/1609/5-towing-mirrors-must-knows.

Personally I have been using strap on types for 40 years - main thing is to remove them when not towing.www.supercheapauto.com.au/p/sca-sca-towing-mirror---clamp-on/342034.html
You must use on both sides of vehicle.

The law is that you have to have towing mirrors if the trailer obscures your rear view from the car's standard mirrors. I have tried a few different types but now use the Millenco Grand Aero which I can recommend.

I remember many moons back that if any towed vehicle was wider than the towing vehicle you HAVE TO HAVE towing mirrors fitted.

Maybe just fit them best to be safe.

Thanks a lot guys