My tonneau cover with zip is not watertight.
That is the reason for always using the storm cover whenever hood down and possible rain at parking outside.
Same here Heinz , when I finally decide to treat my car to a new tonneau I am going to get a flap fitted to cover the zip and gain some protection, that will minimise water ingress from the centre. However I find that with the side screens in place the rain goes down the sides of the tonneau and into the cockpit. I can't find a way to minimise this without removing the side screens, which is why I do as you do and utilise the storm cover whenever I can f there is a risk of heavy rain.
