[Number 4]

My two 30-gal tanks walked off while my trailer was sitting on a pad next to my driveway in a residential neighborhood. I cabled and locked the replacement tanks but then an RV tech explained an alternate theft prevention method. Flatten one of the two steel "wings" that are welded to the hold-down nut, then bend it back up at about the halfway point. Drill a hole through the flat part of that wing and a corresponding hole through the U-shaped steel bar with notches that secure the tank flanges. Crank everything down, line up the holes and install a padlock with a long shackle and lock 'em up tight.