Being in Phoenix, our 19-foot Bambi sits outside in 110+ degree weather every summer; and we don't use the air conditioner or open the ceiling vents. We bought it new in 1995 and the inside seems to have survived the heat just fine, sort of like what you'd expect with your car or tow vehicle. We put sun shades in the windows, but I'm unsure whether that really helps much. It mainly keeps people from snooping inside, which is pretty difficult anyway due to the heavily smoked glass.
In the past couple of years, we have had a couple of weeks each year when it is 115-118 degrees, so we are not particularly concerned about it sitting in the heat. I would worry more about the severe cold and snow in the northern states. We don't worry about pipes freezing or water damage. Also, hail is extremely rare in Phoenix; and if we ever see any, pea or marble size is about as big as it gets.