The spares accumulated over my years of R4 ownership are steadily being sold off through eBay and amongst the items yet to be listed is a towbar with detachable ball but without electrics. I bought it to fit to my 4 as protection against those who 'park by feel' (hence the absence of electrics).
It's a home design made from very heavy gauge angle iron sections and I was informed when I bought it that, unlike a factory-made towbar, it could be fitted without having to disturb the tank. It would benefit from being stripped and repainted - I never got round to it.