Thank you Scott,Yes, coach air return in ceiling and cold air out should have roughly 20 degree difference if all other things are equal. As others have said though, windows uncovered, poor insulation, direct sun all will affect the interior temp. We put up window awnings on our full wall slide windows and noticed a big difference in the heat coming in those windows and could still see out. If a full blackout is an option then reflectx is an option. Keeping the sun/heat off the glass and slide roof is more effective than trying to contain the heat it causes once it gets inside, so anything you can do on the outside will help.
I'll finish installation of my windows and look into getting awnings on my slide outs.
What is your favorite AC maker and model?