Thanks to Des for the advice about de Graff and the docking bars.
Got them for £141 and fitted them very easily.
Only recovered twice since I've fitted them but it went very easily, especially when the boat went a bit to one side so I pushed it back with the strap attached which centred it and up it came.
So the docking bars get a thumbs up so far. The only snag is they add width to an already wide trailor and getting down the road to the lymington slipway was a nightmare.