08 Rockwood Roo Hot Water Heater Question.....

You have a SUBURBAN water heater

It uses an 3/4" NPT 'anode rod' that screws into the drain hole (Atwood uses the 1/2" Nylon plug)

Tank is Steel GLASS-LINED tank
DO NOT use external heat or go hammering on tank.

Drain anode rod hex head requires a 1 1/16" socket (6 point best)
Along with a 6 1/2" extension
1/2" drive and breaker bar

Try to tighten plug a bit at first then unscrew

(Water supply off....pressure relieved !!)