Someone here on the list explained last summer how spraying on water
repellents on the canvass is a real no no and will make the canvas
unbreathable and that the canvass is naturally water repellent. 

I have sprayed my canvass with water repellent and now it gets clammy up
there and I wished I hadn't. Canvass is naturally waterprooof, according to
last summer's post.