The longer trailers move more, I've found. On my 35 ft Windjammer, I never was able to eliminate the movement and is bouncier than my old 25 footer. I've gotten ideas from this forum and the Forest River forum on how to mitigate it, but I would have to invest $$ to reduce it. We just got used to the extra movement and don't care any more. One suggestion that worked very well was to put a scissor jack under one axle to support the middle of the trailer to stop the flex in the middle and I've done it a couple times when there were a lot of people in the trailer. Otherwise I don't bother.
BTW, I learned there is back-in-forth movement, and up and down movement, and require different strategies to mitigate, but that is a topic for another day.