Di-Directional Isolator

You have some problems that you need to locate and solve. The fact that you are burning out isolators is just a side effect of the problem. When you start the engine, your coach battery should be getting power from the alternator and charge to full power. Maybe the isolator isn't built for the amperage that your alternator is pushing. I switched to an old style solenoid style isolator instead of the solid state isolator and haven't had a problem.

Check all of your connections and make sure that they are clean and tight.