Our 364 sq ft 5th wheel has one 15,000 btu A/C unit. In 90 degree heat we can keep the inside at 70 degrees. We have the patio awning deployed as well as awning on each window. Inside we have our mini blinds down and turned so that the sun does not come in through the window. Our door stays closed as much as possible. We set the thermostat at 55 degrees.
We use fans to direct cold air to hot spots within our RV.
The A/C unit stays on 24/7 as long as the heat outside is over 80 degrees during the day. If we get cold we put on jackets rather than turn off the A/C. My goal is to keep everything inside the RV cold (cabinets, walls, counters, furniture...etc) to keep the A/C unit from having to work harder at maintaining a comfortable temperature.