Mike , from Ladder Safety Devices / Lansford Access Ltd /999 Ladders. They do a couple but these are the best. Aprox £500
The bar rests on the bottom of the roof and then the roof ladder clamps onto that
As you know connys come in all different shapes & sizes and these will reach most but not all .
Personally I would not put any PW onto a conny , leave yourself open for complaints !
Ed