Thanks for all the great responses.
Unfortunately the Samsung mw620wa model is no longer available, parts only.
Do you have a model number for either of your Panasonic Inverter microwaves ? My initial search found the smallest one to be 1.2cu ft which would correspond to 1200 Watts. That is probably not it.
Other option is to go with a good inverter but the distance from the battery bank to the converter would necessitate access through the floor and a 4/0 cable to minimize voltage drop. Not my first choice.