Odor from the hot water system is not a service problem and many water supplies contain sufficient amounts of sulphur to produce an odor.
The odor is similar to rotten eggs and is often referred to as "sulphur water." Sulphur water is not harmful - only unpleasant to smell. Sulphur water can be caused by a chemical action or by bacteria. The key to eliminating this smell is heavy chlorination of the water system. Add about six (6) ounces of chlorine (common household liquid bleach) to each 10 gallons in the water tank. Then run the heavily chlorinated water throughout the system, opening each faucet one at a time until you smell the chlorine.
Let the RV sit a few days and the chlorine should take care of the problem. Then you will need to take care of the chlorine by flushing the water system. If you don't have a water filtration system that removes chlorine, you may have a problem getting rid of the chlorine taste.
You might consider adding such a system because it allows you to keep water chlorinated and this prevents several problems, including sulphur water. Chlorination also takes care of other types of bacteria and viruses.