What edible solution can I cover bread in to make it waterproof?
Carnuba Wax. It's edible and waterproof. In my childhood they used to sell a candy bottle made of Carnuba Wax with colored sugar water in it. You'd bite the top off, drink the sugar water and chew on the wax until you got tired. 

http://chemistry.about.com/od/foodchemistryfaqs/f/carnauba-wax.htm