It can be done but might be quite expensive. Go look at the higher end RV's with fully ducted air to see how they're layed out. Fully ducted is where nothing of the a/c unit can be seen in the ceiling. I won't have another RV that isn't fully ducted. Mine has two return ducts on the sides of the ceiling near the walls. Others have circular ducts opposite the exhaust ducts down the middle of the RV. You might just want to upgrade your RV to a better unit.
2013 Chevy 3500HD CC dually
2014 Voltage 3600 toy hauler
2019 RZR 1000XP TRE