How do you determine the proper size, placement and type of anode (magnesium/zinc?) to install on a steel storm shelter? One is 5'x5' the other 5'x10' both are 10 gauge.I've read that too large an anode will "push" the paint off and too small of one won't do it's job. I'd like to have them inside if possible so that they can be replaced when worn.Thanks in advance.