You have a couple of choices, and "paint" is not one of them.

George Dyson sells liquid hypalon for about $50 a gallon. This is a liquid synthetic rubber, so it is flexible, rolls (not folds) well and has been proven for years on Klepper kayaks.

You would usually put this on a synthetic fabric -- nylon, polyester, dacron -- but it could go on canvas, too. Dyson also sells these fabrics in various weights. I got a sample of a fabric from him which looked like it was as thick and strong as the seat belts in my car. He has others which are lighter weight. You pick and chose depending on how much you want to spend and how heavy the boat can be

The other choice is to go with a fabric that is already coated with flexible PVC (vinyl). This type of fabric is commonly sold for awnings. you can check the McMaster-Carr catalog (www.mcmaster.com, or www.mcmastercarr, I think)

Get something that is 17 to 25 ounces per square yard. These usually come in colors, so you don't have to paint them. You have no extra charge for coatings. They are highly UV resistant, and you can usually sew your pieces together, or you can use a solvent and glue the pieces together. The material can also be heat sealed, but it takes some special equipment to do that properly. With modest application of heat it will heat-shrink slightly so you can pull out some wrinkles.

Hope this helps.

PGJ