In addition to using reflectix to cover the front windshield, we hang thick blankets from the front bed (lowering it slightly, tucking the edge of the blanket, then raising the bed again to hold it tight). This creates an insulating curtain further blocking off the heat coming in through the front cab as well as restricting the cooling area. We also use insulated foil covered pillows made to stuff into the fantastic fan vents to block heat from pouring in from the roof. I also tuck another panel of reflectix behind the blinds for the side windows facing the sun.
Always try to take advantage of shade from trees and extend your awning to throw shade over the side of your rig.
There are some videos on how to inspect and plug air leaks to prevent the cool air from your air conditioner from mixing with the hot air being pumped out (apparently the two air flows run counter current to each other and sometimes the installers fail to tape over the gaps to prevent them from mixing)
Of course the most effective cooling method is to alter your plans and deliberately head for areas with cooler weather
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