Replacing microwave, model no longer made

RV Microwaves come in 2x2 types (Several different models and featurs in one of those 2 but they all fall under the umbrella)

The first 2 is "Standard House Microwaves, Bearing the manufacturer's name" IE: Samsung, GE, Panasonic, Tappin, LG
v/s
Standard House Models bearing an alternate name (My Dometic, is really a LG (Lousy GOODS) or rather it was till I modified it so it will work properly, now it's a Modified LG and works well, (one GE part, one engineering change).

This is the "2" that come in assorted models, sizes and features (like conveciton/microwave, Half-time and so on).

The second 2 is

Modified for RV use v/s Not modified.

On my LG (Which was modified for RV use) The hot air exhaust (yes Microwaves have that) was through the top. This would have quickly totted the cabinet in which it's mounted, So they added some sheet metal to duct it out the front, and of course put a front "panel" around it (Collar?)

The vintage Tappin I had at home would not have needed this mod as it exhausted front to start with.

(I really liked that Tappin).

Some RV makers vent the cabinet instead of modifying the Microwave.

So, what should you do?

Get one that fits, Forget the make and model (Avoid Lousy Goods) but get one that fits.

Find out where it spits out hot, moisture laden, air and if needed pipe it to a safe area.

I did note in the manual that it wants me to cut a 3"x7" opening on top of the cabinet. This is probably what you are talking about for venting the heat. There is no way to do that as the ceiling is there. To the side is the exterior wall and the otherside is a cabinet. The microwave cabinet has a 2" hole in it already for the power cord to pass thru the adjoining wall into a cabinet and plugs into the 110v recepticle. I wonder if that is enough? I could cut another hole in the adjoing cabinet wall and keep the next door cabinet open while using the microwave.