I’d think most any trailer would have a degree of flexing involved with the roads we have ...
... and if planned for, might do less damage than a totally stiff chassis/cab ... seems Foamies would have a bit of give to them , less likely to shake apart, and the “sock" ever holding it all together ... Even Airplanes are made to flex a bit ... all planned ... better flex than break , which would probably require a LOT of TD miles , or ten minutes down my street/road