One simple and quick way I can think of is put it in a balloon with the cord coming out the end you'd tie off. Use a zip tie at that end and if possible face that end down just to make sure no water could get in. I'm sure there is an easier, more sophisticated manner of doing it but thinking back to weatherproofing electronics in R/C vehicles this is one method. If it works for that don't see why it wouldn't work in this application too.