Ah, yeah you'll need that sticker then.
I imported mine from Canada in 2016, and it's a 1991, so it had just hit the 25-year mark. There was actually some confusion as to whether it needed to be 25 years to the day
, or just to the year, and it still had a month to go. I bought it to make sure someone else didn't, then put it in storage as close to the border as possible, figuring I'd come back in a month, when it was 25 years old to the day. I stopped in on my way south to make sure I had all the correct paper work for when the time came, and the agent at the crossing said he thought year was all that mattered so I went back the half hour and grabbed it and drove back over the border with it.
You'd think there'd be a clear-cut answer but really there isn't. As long as you walk out with stamped papers, you're good! It does need to be 25 years or older or have the sticker, and you need one importing form. Those are for sure, even though at some border crossings you might be able to sneak through without one or the other. But you need them to title
the trailer in the US so it's best not to. But other than those two things, what's required will vary depending on the crossing, who's working that day and what mood they're in. I had heard they'd need to inspect it but they never even looked out the window at it.