I did take pics but not a lot. I'll try to describe as I go here.
This pic is the inside of the cabinet. Note the pre-existing 110V outlet in the back right side of the cabinet.
I started by drilling 2, -1/4" pilot holes from the inside of the cabinet, 2" from the cabinet bottom. This gave me orientation to take measurements on the outside. Once my lines were drawn, I drilled a 2" hole with a hole saw to start my cut.
Once the hole was cut through the trailer wall, I went inside and cut the cabinet out. I left the bottom lip of the cabinet because that lifts the front of the AC to allow for drainage. I was then able to insert the AC from the inside.
When cutting the outside wall. I found that it cut very easily and it was very clear when I came to any framing. It was like hitting a brick wall with the fine tooth cutting blade. That told me where to stop and actually made the job easier than I expected.
I cut the wall outward until I hit the framing. This left me about 2" on the right (from the outside) and 5" on the left. There is a frame member on the left that I left in but there is still 3" of cabinet that can be opened up. I will Open the remaining 2" (leaving in the 1" frame member), if I feel the need for additional air flow.
The openings on the sides are for outside air intake to cool the condenser.
After I water-proof the cabinet and install the outside grilles, I will put 2 pieces of sheet aluminum (painted to match the trailer) on piano hinges so that they can be opened up while the AC is running. These will act as baffles (like the pieces of cardboard that you see in this pic) to keep the hot air that is exhausting from the back of the AC from being recirculated back into the cabinet.
Notice in this picture, I cut out the louvered vents on the side of the AC housing to allow for increased air flow.
I feel that the reason that so many people have issues with these side mount AC units is because the factory may not have allowed enough outside air flow for the condenser. There is also nothing to keep the hot exhaust from being recirculated back into the condenser. I'm a little surprised that they work at all, the way that they are installeded.
The AC is working quite effectively with those cardboard baffles. Without them, it was struggling.
I will put 1, 15"x 18" grille behind the AC unit for the exhaust and 1, 15"x10" on either side of the AC for fresh air intake.
I'll post more pics when I'm finished.