Very nice. I have been following this one closely, and plan to utilize many of your techniques.
I recently scored a 2 year old GE 6100BTU unit that has the digital control panel on it. I will be extending the control unit into my camper by extending the 7 wires that connect it. The control unit will mount in the forward wall of the camper.
I have had trouble locating marine deck plates locally, but discovered that a plumbing drain for showers from the local hardware store, combined with a rubber hose coupler will actually work perfectly for me.
Remove the drain grate on top, and the rubber coupler slides VERY snugly inside that. The large nut on the backside gets removed entirely, and you mount 2 or three screws through the flange into the trailer.
In my case, my AC will be perma-mounted to the tongue of the trailer, and the duct-work for the cold supply lines will be 2 1/2" flexible exhaust pipe. Cover it all with a box and call it good.
I look forward to your changes with the PWM and will stay tuned.