A/C effectiveness for rear bed

We are thinking about a TM purchase and since we will be traveling in the Southeast most of the time, I have some a/c concerns. How well does the roof mounted a/c cool the extremities (beds) of the trailer. I know that some older TMs had a roof channel to direct the cool air to the rear bed. Is that still an option. It seems to me that the air will be cool in the middle of the trailer but warmer at the beds (ends), and I prefer cooler sleeping temperatures.