These products are not universal. There are different lengths and sizes of anode rod, and your hot water heater might need a unique size that does not match common sizes. RV water tanks are often smaller as well and can need different size anode rods. When looking at an RV water heater anode rod aluminum vs. magnesium, you will need to consider the side of the unit and the kind of water that you are using in it. If you are running water that is very soft or very hard, this can change your buying decision for the type of anode rod that you need.