OK, so you have the 623L model. Since you don't have any in roof ducting from the A/C and you also don't have an integrated thermostat, it becomes very easy. Many Airstreamers (older non-ducted models) are installing
TOSOT A/C units. These are made by Gree and everyone who has one seems to like them. They are exceptionally quiet and Installation would be a couple of hours, old one off and new one on. They can be ordered with or without a soft start unit, and are heat pump design, no electric heating element, but actual heat pump, which is a good backup to your furnace.
My second choice would be a
RecPro Houghton unit. They have a number of different models, including some low profile ones. Heat pump is an option, as is soft start. I have a RecPro Houghton 9500 btu model (too small for your 23 ft RV most likely) but there are several larger units. The 9500 works well for me in my Bigfoot 21 foot trailer, which has a floorplan quite similar to your Trend.
Both the TOSOT and the RecPro units have digital controls in the ceiling unit, plus a handheld remote. The TOSOT unit is radio frequency connected to the ceiling unit (probably bluetooth) and does not need to be pointed at the ceiling unit. The RecPro models are infra red (IR) like your TV and must be pointed at the ceiling unit for it to work properly.
While the Furrion unit has good specs, I'm not impressed with the inside ceiling distribution unit. Yes, its nearly flush with the ceiling, doesn't intrude on head room, but it basically blows straight down, cold air in one location, thats it. The TOSOT and RecPro units have air distribution that blows fore and aft, and that can be adjusted, so you can put more up front during the day, and more in the back at night, or spread it out evenly. The ceiling units typically don't hang down more than 2 inches. My dislike with the Furrion is.......... Lippert. They have never bought out another company that they didn't screw up the product line in some way. It might be a good unit, dunno. Be aware, the inside ceiling air distribution is ordered and priced separately so include the price of it when comparing dollars with other units.