I've discovered the synthetic rubber coating sprays and they appear to be very promising for waterproofing pretty much anything you need to. I am wondering if there is a reason why in all videos I've found, the coating is applied on the external surface of the material. It would make much more sense to me to turn the bag inside out and spray it from the inside. It looks to me that in this way you achieve the result of waterproofing without altering the look of the bag in question. In addition, there is another advantage in the presence of the bag's fabric as an extra layer of protection for the rubber coating from scratching, cutting, etc. It may very well be that my reasoning is flawed due to inexperience in these matters.