I don't think you're correct on that. I couldn't run a 12 volt fridge at 10 amps for more than 5-6 hours on one house battery.
I had a 3000 watt inverter and if it was only pulling 15---20 amps I should have been able to run a 120 volt microwave or air conditioner off the house batteries for a few hours---but no way it would happen. With the engine idling it couldn't supply 2000 watts at 120 volts without a deficit.
Here's an inverter kit with 300 amp fuse
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www.theinverterstore.com ··· kit.html