If you get the appropriate chain, move them closer together, and crosschain the front and back of each to the deck. In real life they usually have solid Drings welded to the chassis for tie down purposes.
I move the smaller ones with my towtruck, and they also want me to have the boom brought in closer, usually with a block of wood under the bucket to save my deck from getting hammered everytime I hit a bump lol. The ones I move though are only 8-12000 pounds though.