Two thoughts
1) house microwaves, vent to the back, Rv microwaves to the top. I personally did not want one, that vented to the back. As there would be no room for it to vent properly in the RV I believe the dimensions on the below would work fine for you, given what you stated.
2) Camping World carries the dometic brand, that should fit your needs. Put one in a few years back ( it was over the range as well}, no complaints