We fought this every summer for years in several different rv's. We worked camp at a place that had well water. All was well for a few months, every summer, then the smell came. I used to drain the hot water heater, disconnect the water hose, fill the water hose up with bleach, hook hose back up to get the bleach in the water heater, ran bleached water through all the hot water fixtures, then repeated the process with baking powder. We would have non sulfur smelling water for about a week, then it was back. Our solution, hook up to city water or if not possible go to a town and get city water, do above only use city water instead of bleach in hot water heater. The clorine in the water seems to freshen it up immediately and lasts for a long time. When we get to a town we don't even drain the hot water heater we just hook our water hose to city water, run some hot water and the smell is gone forever. Works for us everytime.