400 watt inverters are not going to power microwaves or coffee pots
plenty of companies to start with have apu's and big inverters
your in the heart of most shipping lanes
check out Magnum
When the 400W inverter is plugged in to a 12V socket all you get is 150W.
400W is only available if you connect it directly to the battery via the cables.
150W will power a computer, charging devices, TV.
Most other things that don't take a lot of power, like a lunchbox oven or cooler, run off the 12V plug.