Ah got it!I didn't describe that well.
I measured the distance from the surface of the board to the metal backbox and marked that distance on the side of the PB box then cut off at that mark, removing the back of the PB box and creating a sleeve
View attachment 405788
If the panels are 21mm, would t I end up cutting some of the lug on the PB box too? In my situation, do you think the galvanised extension boxes would work better?
