I always deepen those grooves a bit with the sharp corner of a small file. Then, they work fine as long as your strike-anywheres are fresh. Really, though, if the matchsafe is wet, there's almost no way to prevent a drop or two of water from getting inside when you open it. It should be wiped as dry as possible, and sheltered as well as possible, before opening it. Frankly, I would rather bank on a fresh Cricket butane lighter and a candle as a firestarter. I have had stellar experience with those even at 8000 feet or so.