A few people wrote to say their posters arrived with some bent edges, and that confused me since I was very careful with each poster and I taped each mailing tube shut to prevent loss or tampering.
But I saw a recent photo posted by Jinx723 on Hisstank.com (Thank you!), and although nobody on that forum thread said much about it, I do see the issue and I will take steps to prevent this. http://www.hisstank.com/forum/g-i-joe-general-discussion/342314-awesome-g-i-joe-poster.html
When each poster is rolled up in the tube, the top and bottom sides are facing the ends of the tubes and have some wiggle room. With an excess of activity during whatever sorting and processing that USPS does, that wiggle room might become a liability. It probably could have been avoided with foam blocks or bubble blisters on each side.
Sorry, guys, I've never actually mailed tubes before, so I didn't anticipate the amount of abuse to expect during shipment. From this point on I'll be adding bubble wrap on each side of the mailing tubes to lock the posters in safely.
On reflection, however, I'm glad I left a quarter-inch border around each picture as a buffer zone for just this kind of unpredictable stuff.