Am I to understand that your friend has his RV covered with a storage type fabric protective cover and runs the AC unit while it is covered?
As the AC units need to move air in the external unit in order to transfer heat, I would not recommend that. Sounds like a good way to overheat the AC unit.
Current vehicle list: 17 RAM 3500 4x4 Cummins Aisin 4.10, 16 Flagstaff 832IKBS, 14 RAM 1500 4x4 Hemi 3.92 Bilstein 5100's Derale oil cooler, 97 F150 4x4 5.4L 278,000 miles, 80 Firebird Esprit Aussie Burnout Car https://youtu.be/v06VjII7HmE
, 78 Harley Davidson FX 79,000 miles dad bought new, 71 El Camino ZZ3 TH400 12-Bolt, 37 Ford 3 window 502 Chevy dad built
Days Camped: 2016: 43, 2017: 83, 2018: 44, 2019: 78