FWIW, our bus has the hot WX package; 2 AC units, white roof, tinted windows and extra insulation.
Today it was parked in direct sun, all windows and doors shut all day. 1/2 the curtains were open. No AC or fans on. The rear of the bus was facing the SW.
Ambient high temp. was 78.8 with a slight breeze, at that temp. inside was 78.5.