Do you have the 15k optional unit in the rear? We do and it got plenty of air from the rear ac up to the front to keep it cool. Of course you will not get the same amount of air as the rear (static pressure limitations) but it was enough to keep it cool. What will help is if you close down the dampers a bit on the grilles (they're all adjustable like your house) in the back so that more air gets to the front. Might have to play with them a bit until you get it just right.
We had the rear ac go out on this last trip so we only had the front ac left. It's the smaller unit so it doesn't push much air at all to the back even with the front grilles closed down. So we set a fan on the floor to throw air to the back and we got along fine.
2018 Coachmen Chaparral 360IBL
2008 Ford F250, V10, 4.30