"is there anyway to install a wall thermostat?" The bottom line answer is yes. Factory installed RV A/C units with t'stat are not different in operational design than an RV A/C unit without t'stat. The difference is that units with a wall mounted t'stat have a different electrical control box then a non wall t'stat unit. This box is mounted up in the A/C unit behind the Air Distribution Box, or ADB, which is the large plastic thing with the filter in it and vents for the cooled air to come out as in yours is. Can your new dealer mounted 13.5K A/C unit be converted to operate with a wall mounted t'stat so that the fan shuts down along with the compressor when the inside ambient air temp has been satisfied--yes it can, but it will be quite costly. First you would need a new ADB, then the control box, a wall mounted t'stat and additional wiring ran between the t'stat and A/C unit. Hiding these t'stat wires in the wall and ceiling is not easy at all but do-able.
2015 FR Freedom Express 310BHDS pushing a 2014 GMC Sierra CC