There really is not much "Special" about RV microwaves.
My Rig came with a Dometic Microwave
Turn out it was made by LG (Lucky Goldstar, if a Goldstar works you are very lucky, I was not and had to modify it, now 16 years later it still works but it's part GE and part ME and the rest is LG)
Dometic did add a bit of sheet metal to route the exhaust air (yes they exhaust air) to where they wanted it to go .
If your microwave is "enclosed" in a cabinety (Built in is another word) you may need to do some metal work with the exhaust air. that's all.