For desert conditions single 13.5 and even single 15 won't cut it. Be sure the coils are clean. We can provide instructions. Isolate the cockpit with heavy blankets or sheet Reflectix and put foam insulation in the ceiling vents.
If a lot of your coach is black I can see that being a problem. Just not a dark a/c shroud. The a/c pulls air from rear to front. Once through the condenser core it spills out the sides. Be sure air that's been through the condenser can't get back around the ends or the condenser to heat it. If this part isn't clear I can link you to a thread about it.