Its been interesting reading everyones thoughts on this topic. I agree that the container must be the first line of defense against moisture, but I still like a good quality plastic bag (not a baggie) as a backup.
I have had good luck with the plano plastic ammon boxes. The smaller ones are less than 10 bucks and are easy to paint since I like to do my own custom camoflage. The first one I put out a year ago I just covered with some crappy camo tape. On the annual maintenance run last week, the tape had faded somewhat but the container was in perfect condition and the contents were dry as a bone. For the price they seem like a good alternative to the metal boxes ... although the metal ones are clearly the best.
BTW, what seems to be the best camo tape to use? I've had mixed results with the several brands I've tried. I have seen a Gorilla Glue camo tape that looks good but I haven't tried it.