Unfortunately, most of the thermal barriers and such are marketing hype. They may be marginally effective, but there's only so much you can do with reflective bubble wrap and a few inches of insulation when battling the massive energy output of Big Red.
Probably a lot you can do to help out the AC.
1. Check for air flow coming from around inside speakers, antenna crank handle, etc. This is an indicator the AC vents aren't sealed properly. Take one of the vents down and see if there's any tape between the duct and the ceiling. If not, air is probably being blown into the roof cavity where it's exiting around your speakers and other ceiling openings. Use a good metal/foil based tape (feels like thick aluminum foil---super sticky) and use small strips to seal the area around the vent. Do the same for all vents and you should see a bit of a difference in cooling capacity.
2. Pull your intake vents and see if they're sealed. There should NOT be a gap between the ceiling and the return air duct. If there is, seal it using the same method described above. A gap will pull warmer or hotter air from your "attic" into the return duct, making your AC work harder to cool the return air.
3. Check your solar heat gain. The biggest thing you can do to help your AC is to reduce the amount of solar gain it's trying to compensate for. Put out your awning to shade at least one side of your camper. Cover your windows on the exterior of your camper with some sort of shade fabric. Park in a shaded campsite when possible. Bottom line here is to reduce the amount of solar energy that makes it to the surface of your camper.
Truth be told, I don't know if the new quiet vent systems are any less efficient than a regular AC. There are several factors to consider that may cause your buddy's trailer to be fine and your trailer to be warmer. Number and size of windows, orientation, number of roof penetrations, etc. are all things to consider.
If you're still not satisfied, it may be well worth your comfort and sanity (due to complaining family members) to get a second smaller AC mounted. I recently put an 11K BTU unit in my front bedroom and when combined with the 15K BTU main AC, keeps the camper at whatever temp I set on the thermostat.