I finally freed up one day to work on the teardrop. I finished the electrical upgrade and started the replacement of my (non-working) PetCool with a standard window air conditioner.
My PetCool was mounted in the tongue box. The deconstruction took most of the day since:
a) The installation was built with "permanence" in mind and was never intended to be removed, and
b) The tongue box was more than just a transportation container for the PetCool.
The Petcool was mounted in the tongue box. Supply air was ducted through the back of the tongue box and through the front of the teardrop into the interior headboard cabinets. The return air was ducted from the galley wall, along the bottom of the teardrop, up to the bottom of the tongue box. The tongue box also had a 120v outlet to power the PetCool.
All of the above had to be removed so I can (hopefully) re-use the tongue box for the new window air conditioner. Below are some deconstruction photos:



Because the dimensions are tight, and you won't be able to access controls of the window unit, I plan to ditch the manual rotary switches and use a residential style digital thermostat to control the window unit. To use a residential thermostat, I purchases a 24v DC transformer and relays/contactors for the fan and compressor. I also am installing a "delay on break" relay for the compressor. If there is a power interruption - common at campsites - this relay will prevent startup of the compressor for a time period after power is restored. This is an added level of protection for the compressor.
I have all of the parts for the controls "hack". Next step is to mock it up and test it prior to installation.