Being a plumber you need bleach injection of some sort. Since that will be expensive and you need room for bleach tank, mixing tank etc, its not feasible.
So its sounds like bacterial iron in the water..
I would disconnect from the source and use the fresh water tank onboard. add like 5 teaspoons bleach 6% only to a 50 gallon tank.
Like a pool you want to keep chlorine levels low. 2 ppm <
Remember you are not sanitizing you are just treating. Sanitizing requires large amounts of bleach like 1 cup to 40 gallons..
Also note the bleach will oxidize the iron. And it will settle in the vessels. HWH and fresh tank. Flush these out once a month or so.
