http://www.otterbox.com/waterproof-cases
This may be a better option, if you use epoxy it will be nearly impossible to remove it if you need to add or remove anything from your arduino or even reprogram it
A waterproof case is removable, reusable and will allow easy access to your board to make changes if you need to
Once you put the epoxy on you're pretty much stuck with it, quite literally most of the time
Some of these epoxy compounds or so strong they are used to make electronics virtually tamper proof
A low cost alternative to the otterbox might be a heavy duty vacuum or freezer bag with a large bag of desiccant inside and a custom made gasket for the wires to the outside world
