The 9200 will keep the TC cool enough, and will not cycle on and off as much. Keep in mind, most of the 1300 and larger A/Cs are on RVs twice the inside air space of a TC. It is my understanding, the 1300 btu units are the most popular only because they are cheaper for the RV manufactures do to the volume they buy and stocking one size A/C reduces their inventory.
I am not a Hvac guy. They could explain why you do not want an A/C that is too large.
I think you would get more informed information from the Tech Issues Forum. It is questionable this subject is unique to TCs, but some of it could be unique to TCs. I can move it if you want me too.
Wayne