What is an RV microwave?
The microwave in your RV is the same as any Microwave in a residential setting. If you don't like the hinge on the left...remove the microwave, measure it, go buy one of similar size with the hinge on the right.
I have never seen a microwave with the hinges on the bottom (or top for that matter). Doesn't mean they do not exist, just means I have never seen one.
EDIT: On second thought...yes I have. I seem to remember seeing the door swing downward (bottom hinged). Been a long time...but I do think they exist (or did at one time).