Ta for the thoughts. Have used Fabsil on canvas tents/garden brollies in the past, good stuff.
But thought a more specific item might be better for WAXED cotton. Looking online, a few choices of spray on stuff - same(ish) price. Probably made by the same firm, with different labels on.
Went for the Nikwax one - their stuff has been good for both my walking, cycling & m/cycling gear. Will report back.