The French drain thing did not work at all. There was just not enough height on the wall below the under house vents to have a pipe buried with enough slope to drain down towards the drain. I swear so often I look at some of the bodges around this place and think: who the hell did this? Who thought it would be a good idea to cement a drain in above the ground level? Who says shower tiles need a decent job done on the grout? Why doesn’t the guttering flow towards the downpipes? … I’m getting sidetracked…
So instead I decided on some surface drainage with builders plastic lining the side of the house. I was able to get some shallow drains so the slope could be steep enough without having the ground level go above the under house vents. Sadly I did not think to take photos as I was going, so I only have the finished product!