Another useful microwave is a inverter type. I replaced the 700 watt RCA microwave Escape installed in my 21 with a Panosonic Inverter, a NN-SD372S. It is rated at 950 watts, and, of course, will run at full power when the trailer is connected to a pedestal. A couple of other Escape owners have done the same. I believe Tom (tdf-texas) was the one that discovered the Panasonic & http://www.escapeforum.org/forums/f8...1-a-12511.html
I've run it for short times with a full battery at full power on the inverter without problems, but if you try to run it with a low battery, you will get low input voltage warning buzzer from the inverter, or, even have it shut down if the voltage drops to 10.5V.
The advantage of the inverter microwave is when you select a lower power than full, it only draws that much. i.e. at a power selection of 5 (the range is 0 -10) it only produces 475 watts. A standard microwave when run at 1/2 power still runs at full, but shuts off & on. With a lower than full battery, it may not run even at low power settings. As Brian noted, the end result to provide the same amount of heat will draw the same battery amp hours, but the advantage of the inverter type is you can use it in the morning when your batteries are low by running at a reduced power setting.
Another advantage is using defrost. Most standard microwaves "cook" the thin edges of meat, etc before they defrost the center. Running the defrost setting on the inverter microwave evenly defrosts food.
All in all, a big improvement over the stock microwave. It is more expensive, and while it fits in the 21's microwave cabinet, you do have to trim about 3/4" off the side of the opening. A photo of my installation is at my Escape 21 Modifications page