Two things, you will probably have to measure your specific boat then go to Lowes and find one that will physically fit
you will need an inverter that can handle the electrical load so note the 120 volt wattage on the electrical spec plate on the back of the microwave.
Once you find an inverter that can handle the load (probably ought to plan for some expansion FWIW) you will need to beef up your battery storage capacity to be able to store enough energy to run the inverter for the length of time you want the microwave on. Alternately you can run the engine assuming your alternator has more than 50 amps capacity.
I built a spread sheet that can help sizing all this stuff. If you want a copy email me at
william-roosa@us.army .mil
With all that said you will most likely be looking at a 700 watt oven. That equates to a 1000 watt inverter which will be drawing (700/12=) 58.3 amps with the oven running. Assuming you use it for 5 minutes that is (58.3*(5/60)=) 4.9 AH or not that much for 5 minutes. you will see some ALARMING voltage drops when doing this however but fear not the batts will bounce back once the load stops.
