I recommend Nikwax waterproofing spray or wax. I used on my letahers at Cadwell Friday - and good job too as forgot my oversuoit and it tipped it down most of the day! Stayed dry the entire time. Good for leather/canvas/Nylon/Gore-Tex/pretty much anything. Not spensive either. Can be had from Heine Gerricke or most camping outlets.
Hope this helps.