The best you can hope for is an AC that will deliver a 20 degree reduction from the ambient exterior temperature. Asking a 13,500 BTU unit to accomplish this in any RV over 27’ is unrealistic.
Lots of good tips listed above that you can employ to help your AC but 20 degrees is about as good as it gets. We live in southern Arizona so I’m more than a little familiar with the heat thing. Currently we are the Canyon Point campground on the Mogollon Rim at 7,700’ ... this is how we beat the heat, just go where it isn’t hot. :S
Any 27’ + RV with I’m just a 13,500 BTU AC is telling you that the manufacturer went cheap on this vital system and you can expect many other similar compromises throughout... Run Forrest run!
As always... Opinions and YMMV
:C
