I haven't had the luxury of living in a million-dollar home :), The temperature last night was 83F at 0315 alongside my bed. Foot thick concrete walls and a threat of a 700 dollar electrical bill if I kept this place at 75F and knocked out a chunk of wall for a 16K A/C unit.
Insulation is key and it cannot be effective for RVs with just two inches of space available. Not with today's insulation. House attics can hold eighteen inches to two feet of insulation, walls can contain four inches, and triple windows reduce thermal transfer by magnitudes. Quicksilver was shot with the most expensive foam at the time. Yet it stands no chance when the skin attains temperatures above 150 degreea in direct sunlight. In Quintana Roo, I had three Coleman roof air units functioning to keep the humidity under 60% and temps less than 80 degrees.