Porpoising is caused by not enough weight on the tongue. As you go over bumps the front of the trailer bounces up lifting the rear of the TV. The only time I ever had the trailer porpoise on me was not enough weight on the tongue after boon docking during hunting season. I was returning home with an empty FW tank in front of the axles and an over half full black tank at the rear of the trailer. I hit a section of uneven concrete a couple miles from my exit coming home and the bucking started. The next time coming home I moved weight forward to compensate for the back tank weight and didn't porpoise near my exit like before.