The metal plate the original microwave used is not compatible with the new one. I have been unable to find it's reciprocal. I finally decided to just build it. I cut some 3/4" ugly plywood in the shape of the old metal bracket and attached the wall bracket for the new unit. I don't have a good photo, but there was a piece of 1/2" plywood that the original bracket was attached thru to the wall. This allowed the microwave to stick out beyond the mirrors that are also attached to the wall. I used this piece under the newly installed mounting and I added a few screws to help hold it all to the wall.
Now came the hard part. This microwave had different top mount holes than the original. I had to attach it to the slide, but I didn't want to drill thru the slide as the heads would catch the slide out's gasket and let rain in. So I measured the place the aluminum angle bracket needed to be drilled to use the big microwave bolts and I reused the many small screws to pierce the skin of the microwave.
This left me with a strongly attached bracket, I then lifted the microwave into place (glad I am a 6 foot male, this could be a two person job). I then measured where the bracket ended up and I drilled holes in the new position and screwed (really hard) the other bracket into the top of the slide. It came with two 1 1/2" and two 1 1/4" screws that I reused. This REALLY held the bracket in place, not that I know what I drilled into, but I felt the drill break thru metal at one point. I checked the fiberglass after I screwed it down and there were no punctures on the top of the slide.
The officially hardest part was lining up the brackets. It would have been great if they just did line up, but I had reversed the one bracket to re-use one of the big holes from the original install, so the little holes that the screws go thru to hold the brackets together were no longer in line. I lifted the microwave into place and marked where the new holes should go and then drilled out those holes. If I had been smart I might have screwed the screws into the holes before lifting the microwave again...
It took all my energy to get the holes lined up and screw the screws down, but after 45 minutes I finally had it in place. Plugged it in and then went to microwave last nights left-overs as a reward. Oops!
Unlike the original microwave, this one has the hinge pin in the middle of the door and so when you open it the door extends half a door thickness into the cabinet area. I cannot open the door. Looking at the original photo of the new unit I see it was designed to protrude from the cabinets...
I had no more energy and I just gave up. I later found a piece of 2x3 lumber that I wasn't using and I cut pieces and added them to my sandwich of two plywood boards, just sheetrock screws holding them in place from both sides and then I re-screwed the original plywood board to the wall and re-attached my bracket holding piece to that. I feared this would give the microwave much leverage to pull the screws out of the wall, my only hope was that Airstream had put those screws into the metal of the wall.
I know this looks like the first photo, but if you look closely you'll see a longer tunnel going to the vent. Same steps as before, lifted microwave, measured for the bracket, drilled (with new bit this time, took 1/10th the time), screwed, aligned, attached, plugged into power.
Oh, and I cleaned the kitchen for the first time since this project started. I know Peter has had half a year of nights cooking in his kitchen since this started, but I have other things I am working on fixing in the RV and I am still a year and a half out from taking to the road. At least one more thing checked off my list.
I still have to put back the trim, but since the microwave moved forward I need to cut the trim piece from 6" to 4" and I didn't have a saw at the RV. I am also fearful that this will all come down when I go driving. If it does I'll have to get a microwave intended for RV mounting, like the original with it's metal bracket and diagonal bolts holding the unit in place, not just relying on the top brackets.
Hope this is all useful to the next guy that wants a new microwave in an old Airstream.