Using an inverter in the wrong 'capacity' that it is designed for is not going to get your manufacturer to 'give' you something that the coach was not built with from the factory... though I understand your aggravation. You simply can't use 'heat' devices on an inverter, whether MWS or not - they are not designed for that type of draw. Some higher amp devices are also not suggested to work on inverters, such as the high amp blender you mention - but many times it's the electronics and motors of the devices, not the inverter.
You could try to run your roof air conditioner on your inverter, and it would not work either.
Since most of us with factory supplied MWS Magnum ME2012 inverters don't have the 'issues' you speak of, I can suggest that experience proves that it's not an 'inverter' fault. Use your GENERATOR for high amp draw and heating type devices, that's what it's there for. Using your generator is not a sin.
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