I tow with a VW Touran. VW do not make dedicated extension mirrors. There are three problems
(1) the small gap around edge of mirror means any entry of ext.mirror bracket "lugs" could break mirror. NEVER operate mirror adjustment when ext.mirrors are fitted.
(2) shape of mirror body makes it necessary to take care that strapping-on of ext.mirrors cannot work loose.
(3) angle of nearside mirror body (not adjustable) brings ext.mirror almost level with bottom centre of passenger window.
This requires considerable turning of head to see down side of van. Very tiresome on narrow, winding roads.
To overcome problem (3), I am considering a frame mounted camera on nearside mirror, with a dash-mounted monitor. This will allow nearside check by quick movement of eyes only; result will be less tiring ans safer.