Number of trusses?

I do get blight but it’s generally late in the year, October normally when everything is dying back anyway.

That may be due to the damp? I keep my doors and windows open as much as possible.
iI start hardy annual flowers in September and they would damp off if I shut the doors up and closed in the vents. 
My GH is 20ft long and is pretty tall so I think that makes a huge difference in airflow?