You can verify that your AC is working OK by measuring the air temp right where the cooled air is exiting the AC. My understanding is that a normal temp drop from ambient temp in the camper will be about 19º-20º. If that is the temp drop, you need more AC capacity and less heat gain. The suggestions to reduce heat gain are all on target. Installation of a second AC solves many complaints about inadequate cooling. ACs come in various sizes - 8,000, 11,000, 13,500, 15,000. If you have a 50A trailer you should not have too much trouble removing vent and installing another unit. If you only have a 30A trailer, you will need to be more creative with powering the AC.
2013 Flagstaff 8528IKWS, 2006 F-350 6.0L