Lenora, depending on they type of hot water tank you have you may/may not have an anode. There are 2 manufacturers of hot water tanks for RVs -- one has the anode and the other simply has a plastic plug. If there is indeed an anode, make sure they REPLACE it and FLUSH the tank. Too many dealers simply replace it and don't flush the tank. It's another one of those "easy-peasy" jobs that you can and should learn how to do. BTW, anodes corrode when they're used up -- that's the whole purpose of them -- to take away the mineral deposits in the water (or something like that). So if the dealer says that they're checking it make sure you tell them that you want to see the old one. Keeps them honest.
I replaced my anode this spring after having my trailer for just over 2 years. It was absolutely shocking to see how much gunk was in the bottom of the tank and how little anode was left (read: none!). It's a job that should be done yearly, especially if you're using your rig a lot.
I've gotten pretty passionate about this whole thing, especially when I saw how much stuff was in my tank and the potential for doing major damage to my water lines if I'd let it go any longer.
Sorry for hijacking this ...