cooling hybrid

One way to keep it cooler is to during the hot sunny part of the day, to fold in the beds, and open them again after the sun goes down. That option may or may not work for you, depending on how you use your camper,but it is one way to help keep it cooler.

Most definitely use popupgizmos or the poor mans's version aka solar blankets. When the sun beams down on the canvases, the cover turned shiny side up does wonders to keep the bunkbed areas cool. At night it does the opposite, keep the bunkbed area cozy and warm.