Is the top of your unit painted white? If not consider painting it.
If you were to design a trailer for the poorest possible thermal considerations it would be an Airstream.
There are 2 functions to an AC, temperature reduction and humidity reduction. If you size an AC, larger, for temperature reduction it will short cycle and never reduce humidity.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles