Chris,
Look back to the mirror item in Practical Caravan April 2006 page 239 to see the Repusel Special Mirror ( bottom L. of page )
I bought the identical mirrors some time ago at Barrons Darlington - and certainly not at the eye watering price quoted - for use on a Volvo estate. I sourced extension straps to fit them around the Sedona mirrors after some difficulty and some cost from Repusel but I understand they no longer supply them. So far this is pretty negative comment BUT I did see the self same mirrors on sale at Barrons D'ton about three weeks ago with extra straps included. Maybe if you took the picture from P.C. Mag to your local shop they could help.
If you do get them they need to be clamped on firmly and close to the car body to prevent them "squeezing" off the end of the car mirror. They are easy to remove from the clamps; handy in confined places such as car ferry decks. The Sedona mirrors themselves give a pretty good view down the side of the 'van but the extra width is very handy. Hope this is of help.