mr_andyj wrote:
no such thing as an RV microwave. All are household ones that RV maker made some brackets to match and mount in the opening. Find one that fits in the hole.
In most cases you'll be looking for an "over the counter" microwave, and they are generally 30" wide, although you might find one or two with other sizes. Then you'll have the choice of rear, side, or front venting - many can be changed by simply adjusting a vent baffle. Mounting is similar on pretty much all units: a bracket on the rear of the microwave will mate up with a corresponding bracket on the wall at the installation location, and usually 2 bolts, accessible in the cabinet above the location. May times those bolts will be concealed under whatever shelf lining material that is used to make things look nice in the cabinet.
Removing the microwave is straightforward: unplug it from power and remove the 2 bolts from above, then tilt the top of the microwave toward you and lift the whole thing off the rear bracket. Installing is the opposite: lift it up to engage the rear bracket, then rotate the top up into position and replace the 2 bolts. Plug it in and it should work!