Exciting news!!
Just watched a TV advert for Cuprinol sprayable fence treatment.
It appears that if you spray one side of a wany lap panel fence with the stuff, the other side of the fence changes to feather edge close boarded!
There is a downside - watching the ad, if you spray a feather edge fence brown, the other side goes back to wany lap.
BTW - it would seem that you have to be a FB and laugh uncontrollably to make it work.
How do they do that?