Started to have same issue w/ours a few years ago (hot water). Drained/flushed/re-filled at campground....seemed to take care of it. So I thought. Problem came back. Repeated above till next spring. Upon santizing fresh water system w/ chlorine, I filled hot water tank w/ chlorinated water from fresh water tank. Let set 24 hours, empty, refill fresh water tank (after it was drained), fill hot water tank again from fresh tank. Let sit another 24 hours, drain everything, rinse water tank well w/ angled water wand, refill from house and no problems since past 2 years
OP has picked up some bacteria in water tank and more than likely it's contributing to the sulfur odor