Just towed my new (to me) trailer (2007 Fleetwood Pioneer) home, first time I've towed anything of that size (26') for 15 years or so, and back then, it was only for about a half mile. It went great, I even pulled it into and out of a gas station.
When I got home, I checked around inside, and laying on the couch are two shower curtain rod looking things, aluminum bars with rubber feet on the ends. On the side of these bars are prominent yellow stickers warning that under no circumstances should one ever move the trailer without these bars in place. Huh. I doubt "in place" is laying on the couch.
This is the first trailer I have any experience with that has a slide out. I assume that these bars are some sort of retaining system, that will hold the slide out in during travel. Thank goodness I apparently didn't need them on the 40mi trip home, but the manual (shoddily scanned PDF) from Fleetwood says they're definitely required, and describes these bars exactly.
There's nowhere obvious to place them, however, especially along the top. They would have to be mighty skewed, or placed against the trim along the "lip". There are no flat spots or "open spaces" in the large heavy black rubber seal that goes all the way around the slide out. They're not telescopic or springy at all, and there's no label on the walls that show where they'd go. The manual says "Install transit bars at the top corners of the slide-out when the room is fully retracted." but I can't see any way to make them fit in the corner.
