We talked about this in another thread. Its what GMC considered a safe amp draw on your battery; you can only get out what you put in. You need to think how much current your batteries/alternators can continuously and safely provide.This. Why in the world did they make the amps so low on that bed plug? Dumb.
Existing 400W AC from bed plug draws up to 40amps for a maximum 400W draw.
Lets say you want a 1000/2000/3000 or even 5000W inverter, you need a lot of 12V DC amps going in.
Basic formula: Amps = Watts/Volts
With effeciency factor: Amps =(Watts / Volts) /Efficiency(likely 85%)
1000W AC Inverter Amps = (1000/12)/.85 = 98amps for maximum 1000W draw.
2000W ~ 200Amps etc.