Well, I can see the manufacturer's logic in this...The financial dept. of the company...
"Well, we need to cut costs and weight...I hear that people still can't pull one of our 5ver's with a Prius yet, so how do we make that happen people?"
"We could call Toyota and have them mount a 5th wheel plate to the top of their cars...easy peazy!"
"But what about the weigh issue? We have to find a way to drop the trailer weight to make it so that anyone driving anything can pull one of our trailers."
"Well if weight is the issue, we can take wood out...that's heavy isn't it? I've never been to the factory so I haven't ever seen a real piece of wood that goes into our trailers."
"I've got it! Wood is made of wood...Cardboard is made of wood...or cards...one or the other. If it is made of wood, we can argue that we still use all-wood construction in our trailers. IT is just modified wood. We would have to get with legal on it, have them do a liability analysis, but I think we are in the clear on this. Just substitute "Modified Wood Structural Bracing for the plywood we would normally use, and we are golden. Heck, I might even be able to get a trailer now to pull behind my Prius! I think a 32 footer with 5 slides! My kids will enjoy those once we get parked! Wheeeee!!"
And that, is why there is cardboard behind the cap on your trailer...This is how it begins...or continues.