It's called a sacrificial anode. Try some pin point heat from a small oxy / acet torch at one area of the thread. It may melt some styrofoam but that's okay, and then quickly wind it out ( maybe use two people). Make sure you don't set the place on fire.
That rod is the tank drain . Someone should have told you to drain it at least once a year? How did you winteize the tank without draining it ???
It was a rainy few days at Algonquin Prov park...tarps kept us dry.
Wayne --Belle River (Windsor), Ontario
2013 Sunset Trail Reserve 25RB..
2015 White Chev Silverado 2500HD 4x4 (6.0 l gasser)
2003 Mountain Star 890SBRX Truck Camper