We installed a Dometic cool cat heat pump under one of our twin beds in our 1966
Tradewind restoration. The key issue was distributing the air throughout the trailer. We had a galvanized distribution box fabricated that was installed under the subfloor between frame crosspieces that has 2 inch high compression tubing going from it to various vents through the floor. There is a 15in x 4in return duct in the bathroom closet that feeds under the bulkhead back to the unit. If you wan to see pictures you can go to my restoration blog at annieairstreamrestoration.blogspot.com. It works great for us, providing our AC and heat down to 40 degrees when the thermostat automatically kicks it off and switches to our gas furnace. However, from what I understand from the local Camping World guy that sold us the unit, it doesn't work nearly as well if it is not ducted. It was also a bit involved to design and install so it would work properly, including have to cut a hole in the side of the trailer for the exhaust and intake. We had a compartment door that matched our other doors made so it would not be obvious when we were not using the unit.