4 years ago I bought 5 litres of canvas paint from a well known supplier. Ad said waterproofs correct shade etc. etc.
Big mistake. Applied it to my 9x9 which really was OK but thought I was being clever in sprucing it up.
Paint looked like vehicle paint, smelt like vehicle paint, went on like something from Tate & Lyle and was nothing like the correct shade. Result I have a rigid 9x9 which does n't require a frame. Weighs probably in the region of 3 times MOD spec weight. And won't even fit into a 12 x 12 canvas holdall. Supplier still swears its the right product and still is advertising.
Moral don't waterproof unless absolutely necessary or if you have to, visit a builders merchant and purchase one of the propriety clear waterproofing solutions.
Cheaper and more effective.