I have had good results by reducing the tire pressure till it's noticeably low, tying the bottom of the landing gear to the trailer or flatbed, and then reinflating the tires. That tensions the ties and it's a solid connection. Probably also should tie the tail down with a line to either side of the bed to make a wide angle and pick up any side load.
Did this twice, the last moving an RV-10 to the airport.
Dave