I just taped in the corner. They don't close entirely. But I don't want mine to. I like that they can get moisture that way also and hopefully will vent them somewhat also, WHEN it FINALLY warms up here!
I don't even use any tape at all to close the top to the bottom. I punch a hole just above and below the cut (which divides the top from the bottom), and use a twist-tie to hold it shut. This way there's more air circulation AND more ways for rain and snow to get into the containers.
Gorilla products are wonderful!!! I seem to be a bit "addicted" to my Husky knife, it's got a regular 'knife' side and a razor side, and that's what I use to poke my holes in my milk jugs. What can I say, I'm a girl, and my knife is pink! < =)