The height and narrowness of the exit count. If, for example, the hot air rises up a continually constricting channel this is why most smokestacks are narrower at the top than the bottom it rises with more velocity and force. Despite all these precautions, the rooms will still heat up. The trick is to use a substance that reflects as much heat as possible. Most materials used in building construction, such as brick, stone, wood and such absorb about 90 percent of heat radiation, regardless of their color.
Metals have very low absorption rates.
Those dark mirrory windows you see on commercial structures keep out heat not because they're mirrored, but because of metals suspended in the glass. Something like aluminum foil will reflect back virtually all of the heat radiated on it, but will still absorb heat by conduction. Now you know why baked potatoes in a campfire require aluminum foil wrappers. Think about ways the above information can be used to cool your own home. And if there's a way it'll also fix the portable problem, let the kids at Waianae know about it.