There have been several threads on the basement air. Seems like one of the major problems is the ducting separation that allows cool air to escape rather than go into the RV. Something to think about if air flow is not sufficient coming out of the ducts. I'd suggest you get a thermometer and check air temp at a duct and at the air return. On mine the cool air at the duct is about 20 - 22 degrees cooler than the air going into the return. If there is not much difference in the air temp it should be a unit problem and servicing should have repaired it. My RV will not cool down in hot weather unless the AC is started before it gets hot outside. We spent June, July & August in the south (Florida to California) and it was hot. We ran the unit fan 24 hours a day, during the day the compressor ran all day & at night the compressors would shut down for periods of time. We also used window covers to help block out side heat. When traveling we ran the generator so we could use the basement AC.
Bob, Sandi & Marmaduke the Big Pug and Tasha a Frenchie
SW OREGON Winnebago Outlook Ford V-10
If towing: a 2006 Mini Cooper or 2015 RAM Limited 4X4 or a 86 El Camino on a trailer