We have the same issue. We try to cool down the rear area before bedtime and turn the rear A/C off before bedtime and the front unit on high. Then we close the vents in the front to force more air to the rear.
If warmer, we sleep with a fan.
Then we reverse the logic if trying to watch TV. During the heat of the day, we run both units as required.
Life is a journey, not a destination.
2005 Georgetown 359ts
Bill & Virginia, Kentucky
Nights camped in 2011...78 , 2012...73,
Nights camped in 2013...123, 2014 ...101