So, letterboxers spend so much time talking about what others should put on the inside of your letterbox, that I thought it would be a great idea to discuss the outside. To some this might sound very simple. But there is actually a debate going on as to whether or not you should put a ziplock bag on the outside of the letterbox for extra protection. I will give you the pros and cons of doing such a thing, and ultimately tell you how I feel about the ziplock bags.
First, let me discuss the pros of ziplock bags as protection for your letterbox. (1) If you happen to use a not so good tupperware container for your letterbox, this could be of some help. Depending on where you put your box, you might set your box up flooding. The ziplock bag will help a little to protect your box from being water logged, but........ (2) A ziplock on the outside of your letterbox will help protect your box from ice in the winter. Now, if your box is planted in a location that will be prone to snow and ice, sometimes during the colder months, it does warm up, causing ice to form. If ice gets to your box, it could cause your box to crack and then water will get into your box causing the insides of your letterbox to become damaged.
Now, since I can't think of any other pros for ziplocks on the outside of your box, let me discuss the cons. (1) Ziplock bags attract animals. For what ever reason, they smell the bag and begin to chew on it. Once the animal realizes that plastic doesn't taste as good as it smelled, the damage has already been done and the bag is left with holes. Therefore leaving you with a ziplock bag that no long serves its purpose. (2) Letterboxers that tend to be careless, new and old, may not zip your ziplock back up well enough causing it to fill with water during rain periods. This will then test the durability of the tupperware container you choose. If the container you choose isn't that great, plan on replacing everything inside the box. (3) We take pride in leaving not a trace. If we are putting ziplock bags on the outside of our letterboxes, and they are being chewed, plastic pieces are being littered around the area where the letterbox is planted. We then are leaving a trace.
I am sure there are many other pros and cons, but these are just a few that I came up with. In my opinion, ziplock bags should be kept inside the letterbox. I used to use ziplock bags on the outside of my letterboxes when I started letterboxing 4 years ago, but it didn't take me long to realize that they did nothing. I would find that animals were chewing them apart and not actually doing any good.
In closing, I must also mention one more thing. DO NOT put a ziplock bag around someone elses letterbox, even if you think it needs one. If someone was to do this to one of my boxes, I would be rather upset. Contact the planter and let them know about the condition of their box and whether or not it needs tending to. Replacing a ziplock bag on the inside of the box is different than putting a ziplock bag on the outside.