The plumber will first decide whether a repair makes sense. A burner, thermocouple, gas control, or electric element can often be replaced, and flushing sediment can help an otherwise sound tank. A leaking tank body generally means replacement.
A replacement in Carver needs a plumbing or gas permit from the Building Department, filed on paper with an inspection request form. The inspector works Monday, Wednesday, and Friday with inspections starting at 8, and the license holder makes that call, so ask when it's planned.
In a mobile home, the heater often sits in a small closet, and the new unit has to fit that space and its venting. Switching fuels, for example from oil to propane, adds a tank, a gas line, and possibly another permit.