have a canvas that I use while the boat Is at the dock on a lift. it is a cheap one from walmart. great condition but has some mildew on the inside from sitting outside. can you wash it in a big washing machine with something that will remove the mildew without weakening the fabric? is there something I can spray on after to waterproof it? have a custom canvas that I use for travel. thought that the cheap one would be temperery but can't justify putting the good canvas on.