I am not familiar with the bag you are talking about but from what you are describing I would look for something by Ortlieb. They make many waterproof bags for many different applications. I have seen their motorcycle pannier bags and they look bulletproof. The other company that makes tough waterproof cases is Pelican Products their medium sized cases can be set up like a briefcase and will float 30 lbs of contents.
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When the wolf attacks he will find that some who run with the flock are not sheep!