Our boat had a microwave installed when we bought it. It's on a shelf above the sinks. The AC is strung from the outlet near the icebox inside the cabinet above the stove, through a hole into the trash bin area, then behind the sinks and up the vertical s/s grab bar and onto the shelf. It's a little Sanyo. You would probably want to buy the microwave before installing the shelf. Our install looks factory with teak trim, etc. One end of the shelf sits on a teak rail at the cabin side with three screws into the whiteboard. The other end attaches to a stainless bracket welded to the s/s grab bar.
PSC 34 #305 "Swan"