Air conditioning in new 5th Wheel

Regardless of brand of RV, there maybe an issue with return air not making into the exchange correctly. On all of the RV's I have owned over the past 30 years, I have always taken the air conditioner bezel off inside and foil taped around the sides so air does not get between roof and ceiling. Only the ducting, will be allowed air if you have ducting. Also the, so called plenum between the cold air and the warm return air may need to also be foil taped to keep the air conditioner from just recirculating air that has already been cooled. If your cold air is just sucked back in the return then you are not circulating the cooled air. My last 5er I had to do that on both air conditioners. I keep an infrared thermometer handy to check the vent temps and expect a 20 degree or more differential after about 30 minutes of running it. But I would sure look at the air not being circulated right in the area just under the air conditioner on both units. My dad had a brand new Cardinal and he was having an issue with not cooling correctly. Took it in and they said was all good. I drove 5 hours to his location with my handy dandy foil tape. We took off all vents and bezels and taped the connections between the vent and pathways at the air conditioner and final destinations in the RV and now on 100 degree days, in East Texas, he is in a 68 degree RV. Just my 2 cents.